diff --git a/modules/openapi-generator/src/main/resources/php/ApiException.mustache b/modules/openapi-generator/src/main/resources/php/ApiException.mustache
index 185be1a0a0a2..dcba96b0e43a 100644
--- a/modules/openapi-generator/src/main/resources/php/ApiException.mustache
+++ b/modules/openapi-generator/src/main/resources/php/ApiException.mustache
@@ -34,7 +34,7 @@ class ApiException extends Exception
     /**
      * The HTTP body of the server response either as Json or string.
      *
-     * @var mixed
+     * @var \stdClass|string|null
      */
     protected $responseBody;
 
@@ -48,17 +48,17 @@ class ApiException extends Exception
     /**
      * The deserialized response object
      *
-     * @var $responseObject;
+     * @var \stdClass|string|null
      */
     protected $responseObject;
 
     /**
      * Constructor
      *
-     * @param string        $message         Error message
-     * @param int           $code            HTTP status code
-     * @param string[]|null $responseHeaders HTTP response header
-     * @param mixed         $responseBody    HTTP decoded body of the server response either as \stdClass or string
+     * @param string                $message         Error message
+     * @param int                   $code            HTTP status code
+     * @param string[]|null         $responseHeaders HTTP response header
+     * @param \stdClass|string|null $responseBody    HTTP decoded body of the server response either as \stdClass or string
      */
     public function __construct($message = "", $code = 0, $responseHeaders = [], $responseBody = null)
     {
@@ -80,7 +80,7 @@ class ApiException extends Exception
     /**
      * Gets the HTTP body of the server response either as Json or string
      *
-     * @return mixed HTTP body of the server response either as \stdClass or string
+     * @return \stdClass|string|null HTTP body of the server response either as \stdClass or string
      */
     public function getResponseBody()
     {
diff --git a/modules/openapi-generator/src/main/resources/php/Configuration.mustache b/modules/openapi-generator/src/main/resources/php/Configuration.mustache
index c5885598ae3f..d5244a727bf2 100644
--- a/modules/openapi-generator/src/main/resources/php/Configuration.mustache
+++ b/modules/openapi-generator/src/main/resources/php/Configuration.mustache
@@ -29,6 +29,9 @@ namespace {{invokerPackage}};
  */
 class Configuration
 {
+    /**
+     * @var Configuration
+     */
     private static $defaultConfiguration;
 
     /**
@@ -128,7 +131,7 @@ class Configuration
      *
      * @param string $apiKeyIdentifier API key identifier (authentication scheme)
      *
-     * @return string API key or token
+     * @return null|string API key or token
      */
     public function getApiKey($apiKeyIdentifier)
     {
@@ -154,7 +157,7 @@ class Configuration
      *
      * @param string $apiKeyIdentifier API key identifier (authentication scheme)
      *
-     * @return string
+     * @return null|string
      */
     public function getApiKeyPrefix($apiKeyIdentifier)
     {
@@ -400,7 +403,7 @@ class Configuration
      *
      * @param  string $apiKeyIdentifier name of apikey
      *
-     * @return string API key with the prefix
+     * @return null|string API key with the prefix
      */
     public function getApiKeyWithPrefix($apiKeyIdentifier)
     {
@@ -423,7 +426,7 @@ class Configuration
     /**
      * Returns an array of host settings
      *
-     * @return an array of host settings
+     * @return array an array of host settings
      */
     public function getHostSettings()
     {
@@ -461,9 +464,9 @@ class Configuration
     /**
      * Returns URL based on the index and variables
      *
-     * @param index array index of the host settings
-     * @param variables hash of variable and the corresponding value (optional)
-     * @return URL based on host settings
+     * @param int        $index     index of the host settings
+     * @param array|null $variables hash of variable and the corresponding value (optional)
+     * @return string URL based on host settings
      */
     public function getHostFromSettings($index, $variables = null)
     {
diff --git a/modules/openapi-generator/src/main/resources/php/HeaderSelector.mustache b/modules/openapi-generator/src/main/resources/php/HeaderSelector.mustache
index 2fdc0ab204fc..5f8e65587279 100644
--- a/modules/openapi-generator/src/main/resources/php/HeaderSelector.mustache
+++ b/modules/openapi-generator/src/main/resources/php/HeaderSelector.mustache
@@ -66,7 +66,7 @@ class HeaderSelector
      *
      * @param string[] $accept Array of header
      *
-     * @return string Accept (e.g. application/json)
+     * @return null|string Accept (e.g. application/json)
      */
     private function selectAcceptHeader($accept)
     {
diff --git a/modules/openapi-generator/src/main/resources/php/ObjectSerializer.mustache b/modules/openapi-generator/src/main/resources/php/ObjectSerializer.mustache
index 2694de44fe76..31dd9fc33764 100644
--- a/modules/openapi-generator/src/main/resources/php/ObjectSerializer.mustache
+++ b/modules/openapi-generator/src/main/resources/php/ObjectSerializer.mustache
@@ -51,20 +51,26 @@ class ObjectSerializer
      * @param string $type   the OpenAPIToolsType of the data
      * @param string $format the format of the OpenAPITools type of the data
      *
-     * @return string|object serialized form of $data
+     * @return scalar|object|array|null serialized form of $data
      */
     public static function sanitizeForSerialization($data, $type = null, $format = null)
     {
         if (is_scalar($data) || null === $data) {
             return $data;
-        } elseif ($data instanceof \DateTime) {
+        }
+
+        if ($data instanceof \DateTime) {
             return ($format === 'date') ? $data->format('Y-m-d') : $data->format(self::$dateTimeFormat);
-        } elseif (is_array($data)) {
+        }
+
+        if (is_array($data)) {
             foreach ($data as $property => $value) {
                 $data[$property] = self::sanitizeForSerialization($value);
             }
             return $data;
-        } elseif (is_object($data)) {
+        }
+
+        if (is_object($data)) {
             $values = [];
             if ($data instanceof ModelInterface) {
                 $formats = $data::openAPIFormats();
@@ -250,7 +256,9 @@ class ObjectSerializer
     {
         if (null === $data) {
             return null;
-        } elseif (strcasecmp(substr($class, -2), '[]') === 0) {
+        }
+
+        if (strcasecmp(substr($class, -2), '[]') === 0) {
             $data = is_string($data) ? json_decode($data) : $data;
             
             if (!is_array($data)) {
@@ -263,7 +271,9 @@ class ObjectSerializer
                 $values[] = self::deserialize($value, $subClass, null);
             }
             return $values;
-        } elseif (substr($class, 0, 4) === 'map[') { // for associative array e.g. map[string,int]
+        }
+
+        if (substr($class, 0, 4) === 'map[') { // for associative array e.g. map[string,int]
             $data = is_string($data) ? json_decode($data) : $data;
             settype($data, 'array');
             $inner = substr($class, 4, -1);
@@ -276,10 +286,14 @@ class ObjectSerializer
                 }
             }
             return $deserialized;
-        } elseif ($class === 'object') {
+        }
+
+        if ($class === 'object') {
             settype($data, 'array');
             return $data;
-        } elseif ($class === '\DateTime') {
+        }
+
+        if ($class === '\DateTime') {
             // Some API's return an invalid, empty string as a
             // date-time property. DateTime::__construct() will return
             // the current time for empty input which is probably not
@@ -291,10 +305,14 @@ class ObjectSerializer
             } else {
                 return null;
             }
-        } elseif (in_array($class, [{{&primitives}}], true)) {
+        }
+
+        if (in_array($class, [{{&primitives}}], true)) {
             settype($data, $class);
             return $data;
-        } elseif ($class === '\SplFileObject') {
+        }
+
+        if ($class === '\SplFileObject') {
             /** @var \Psr\Http\Message\StreamInterface $data */
 
             // determine file name
diff --git a/modules/openapi-generator/src/main/resources/php/api.mustache b/modules/openapi-generator/src/main/resources/php/api.mustache
index 9ec54edeb0d4..a80d08486bda 100644
--- a/modules/openapi-generator/src/main/resources/php/api.mustache
+++ b/modules/openapi-generator/src/main/resources/php/api.mustache
@@ -80,17 +80,17 @@ use {{invokerPackage}}\ObjectSerializer;
     /**
      * Set the host index
      *
-     * @param  int Host index (required)
+     * @param int $hostIndex Host index (required)
      */
-    public function setHostIndex($host_index)
+    public function setHostIndex($hostIndex)
     {
-        $this->hostIndex = $host_index;
+        $this->hostIndex = $hostIndex;
     }
 
     /**
      * Get the host index
      *
-     * @return Host index
+     * @return int Host index
      */
     public function getHostIndex()
     {
diff --git a/modules/openapi-generator/src/main/resources/php/api_test.mustache b/modules/openapi-generator/src/main/resources/php/api_test.mustache
index e8c8905c961c..f46fdbac144b 100644
--- a/modules/openapi-generator/src/main/resources/php/api_test.mustache
+++ b/modules/openapi-generator/src/main/resources/php/api_test.mustache
@@ -16,7 +16,7 @@
  * Please update the test case below to test the endpoint.
  */
 
-namespace {{invokerPackage}};
+namespace {{invokerPackage}}\Test\Api;
 
 use \{{invokerPackage}}\Configuration;
 use \{{invokerPackage}}\ApiException;
@@ -71,6 +71,8 @@ use PHPUnit\Framework\TestCase;
      */
     public function test{{vendorExtensions.x-test-operation-id}}()
     {
+        // TODO: implement
+        $this->markTestIncomplete('Not implemented');
     }
     {{/operation}}
 }
diff --git a/modules/openapi-generator/src/main/resources/php/composer.mustache b/modules/openapi-generator/src/main/resources/php/composer.mustache
index fdfd0e2438aa..265bd713d521 100644
--- a/modules/openapi-generator/src/main/resources/php/composer.mustache
+++ b/modules/openapi-generator/src/main/resources/php/composer.mustache
@@ -36,6 +36,6 @@
         "psr-4": { "{{escapedInvokerPackage}}\\" : "{{srcBasePath}}/" }
     },
     "autoload-dev": {
-        "psr-4": { "{{escapedInvokerPackage}}\\" : "{{testBasePath}}/" }
+        "psr-4": { "{{escapedInvokerPackage}}\\Test\\" : "{{testBasePath}}/" }
     }
 }
diff --git a/modules/openapi-generator/src/main/resources/php/model.mustache b/modules/openapi-generator/src/main/resources/php/model.mustache
index 45157dd05209..3c0b819822cb 100644
--- a/modules/openapi-generator/src/main/resources/php/model.mustache
+++ b/modules/openapi-generator/src/main/resources/php/model.mustache
@@ -38,6 +38,11 @@ use \{{invokerPackage}}\ObjectSerializer;
  * @package  {{invokerPackage}}
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+{{^isEnum}}
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
+{{/isEnum}}
  */
 {{#isEnum}}{{>model_enum}}{{/isEnum}}{{^isEnum}}{{>model_generic}}{{/isEnum}}
 {{/model}}{{/models}}
diff --git a/modules/openapi-generator/src/main/resources/php/model_generic.mustache b/modules/openapi-generator/src/main/resources/php/model_generic.mustache
index adc72e548797..408027158297 100644
--- a/modules/openapi-generator/src/main/resources/php/model_generic.mustache
+++ b/modules/openapi-generator/src/main/resources/php/model_generic.mustache
@@ -1,6 +1,6 @@
 class {{classname}} {{#parentSchema}}extends {{{parent}}} {{/parentSchema}}{{^parentSchema}}implements ModelInterface, ArrayAccess{{/parentSchema}}
 {
-    const DISCRIMINATOR = {{#discriminator}}'{{discriminatorName}}'{{/discriminator}}{{^discriminator}}null{{/discriminator}};
+    public const DISCRIMINATOR = {{#discriminator}}'{{discriminatorName}}'{{/discriminator}}{{^discriminator}}null{{/discriminator}};
 
     /**
       * The original name of the model.
@@ -23,6 +23,8 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}} {{/parentSchema}}{{^pa
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         {{#vars}}'{{name}}' => {{#dataFormat}}'{{{dataFormat}}}'{{/dataFormat}}{{^dataFormat}}null{{/dataFormat}}{{#hasMore}},
@@ -161,7 +163,7 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}} {{/parentSchema}}{{^pa
 
         {{/parentSchema}}
         {{#vars}}
-        $this->container['{{name}}'] = isset($data['{{name}}']) ? $data['{{name}}'] : {{#defaultValue}}{{{defaultValue}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}};
+        $this->container['{{name}}'] = $data['{{name}}'] ?? {{#defaultValue}}{{{defaultValue}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}};
         {{/vars}}
         {{#discriminator}}
 
@@ -278,7 +280,7 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}} {{/parentSchema}}{{^pa
      *
      * @param {{dataType}}{{^required}}|null{{/required}} ${{name}}{{#description}} {{{description}}}{{/description}}{{^description}} {{{name}}}{{/description}}
      *
-     * @return $this
+     * @return self
      */
     public function {{setter}}(${{name}})
     {
@@ -362,18 +364,18 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}} {{/parentSchema}}{{^pa
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/modules/openapi-generator/src/main/resources/php/model_test.mustache b/modules/openapi-generator/src/main/resources/php/model_test.mustache
index 848a24b5492b..af9df8ae19b8 100644
--- a/modules/openapi-generator/src/main/resources/php/model_test.mustache
+++ b/modules/openapi-generator/src/main/resources/php/model_test.mustache
@@ -19,7 +19,7 @@
  * Please update the test case below to test the model.
  */
 
-namespace {{invokerPackage}};
+namespace {{invokerPackage}}\Test\Model;
 
 use PHPUnit\Framework\TestCase;
 
@@ -68,6 +68,8 @@ class {{classname}}Test extends TestCase
      */
     public function test{{classname}}()
     {
+        // TODO: implement
+        $this->markTestIncomplete('Not implemented');
     }
 {{#vars}}
 
@@ -76,6 +78,8 @@ class {{classname}}Test extends TestCase
      */
     public function testProperty{{nameInCamelCase}}()
     {
+        // TODO: implement
+        $this->markTestIncomplete('Not implemented');
     }
 {{/vars}}
 }
diff --git a/samples/client/petstore/php/OpenAPIClient-php/composer.json b/samples/client/petstore/php/OpenAPIClient-php/composer.json
index 823e9f92a7b9..08efaa27b921 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/composer.json
+++ b/samples/client/petstore/php/OpenAPIClient-php/composer.json
@@ -33,6 +33,6 @@
         "psr-4": { "OpenAPI\\Client\\" : "lib/" }
     },
     "autoload-dev": {
-        "psr-4": { "OpenAPI\\Client\\" : "test/" }
+        "psr-4": { "OpenAPI\\Client\\Test\\" : "test/" }
     }
 }
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Api/AnotherFakeApi.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Api/AnotherFakeApi.php
index dd8f5426398c..b328c2627c4e 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Api/AnotherFakeApi.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Api/AnotherFakeApi.php
@@ -90,17 +90,17 @@ public function __construct(
     /**
      * Set the host index
      *
-     * @param  int Host index (required)
+     * @param int $hostIndex Host index (required)
      */
-    public function setHostIndex($host_index)
+    public function setHostIndex($hostIndex)
     {
-        $this->hostIndex = $host_index;
+        $this->hostIndex = $hostIndex;
     }
 
     /**
      * Get the host index
      *
-     * @return Host index
+     * @return int Host index
      */
     public function getHostIndex()
     {
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Api/DefaultApi.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Api/DefaultApi.php
index 033120cc5573..00c5f27ccee4 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Api/DefaultApi.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Api/DefaultApi.php
@@ -90,17 +90,17 @@ public function __construct(
     /**
      * Set the host index
      *
-     * @param  int Host index (required)
+     * @param int $hostIndex Host index (required)
      */
-    public function setHostIndex($host_index)
+    public function setHostIndex($hostIndex)
     {
-        $this->hostIndex = $host_index;
+        $this->hostIndex = $hostIndex;
     }
 
     /**
      * Get the host index
      *
-     * @return Host index
+     * @return int Host index
      */
     public function getHostIndex()
     {
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Api/FakeApi.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Api/FakeApi.php
index 026ce251fcec..0b99c8e9aab3 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Api/FakeApi.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Api/FakeApi.php
@@ -90,17 +90,17 @@ public function __construct(
     /**
      * Set the host index
      *
-     * @param  int Host index (required)
+     * @param int $hostIndex Host index (required)
      */
-    public function setHostIndex($host_index)
+    public function setHostIndex($hostIndex)
     {
-        $this->hostIndex = $host_index;
+        $this->hostIndex = $hostIndex;
     }
 
     /**
      * Get the host index
      *
-     * @return Host index
+     * @return int Host index
      */
     public function getHostIndex()
     {
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Api/FakeClassnameTags123Api.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Api/FakeClassnameTags123Api.php
index a17dc5fd6729..094e5e914983 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Api/FakeClassnameTags123Api.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Api/FakeClassnameTags123Api.php
@@ -90,17 +90,17 @@ public function __construct(
     /**
      * Set the host index
      *
-     * @param  int Host index (required)
+     * @param int $hostIndex Host index (required)
      */
-    public function setHostIndex($host_index)
+    public function setHostIndex($hostIndex)
     {
-        $this->hostIndex = $host_index;
+        $this->hostIndex = $hostIndex;
     }
 
     /**
      * Get the host index
      *
-     * @return Host index
+     * @return int Host index
      */
     public function getHostIndex()
     {
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Api/PetApi.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Api/PetApi.php
index 6d8554cce908..e92065f162b2 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Api/PetApi.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Api/PetApi.php
@@ -90,17 +90,17 @@ public function __construct(
     /**
      * Set the host index
      *
-     * @param  int Host index (required)
+     * @param int $hostIndex Host index (required)
      */
-    public function setHostIndex($host_index)
+    public function setHostIndex($hostIndex)
     {
-        $this->hostIndex = $host_index;
+        $this->hostIndex = $hostIndex;
     }
 
     /**
      * Get the host index
      *
-     * @return Host index
+     * @return int Host index
      */
     public function getHostIndex()
     {
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Api/StoreApi.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Api/StoreApi.php
index d05718f74946..d4e853de9c3c 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Api/StoreApi.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Api/StoreApi.php
@@ -90,17 +90,17 @@ public function __construct(
     /**
      * Set the host index
      *
-     * @param  int Host index (required)
+     * @param int $hostIndex Host index (required)
      */
-    public function setHostIndex($host_index)
+    public function setHostIndex($hostIndex)
     {
-        $this->hostIndex = $host_index;
+        $this->hostIndex = $hostIndex;
     }
 
     /**
      * Get the host index
      *
-     * @return Host index
+     * @return int Host index
      */
     public function getHostIndex()
     {
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Api/UserApi.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Api/UserApi.php
index a9fede94b862..5e26aa165b3b 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Api/UserApi.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Api/UserApi.php
@@ -90,17 +90,17 @@ public function __construct(
     /**
      * Set the host index
      *
-     * @param  int Host index (required)
+     * @param int $hostIndex Host index (required)
      */
-    public function setHostIndex($host_index)
+    public function setHostIndex($hostIndex)
     {
-        $this->hostIndex = $host_index;
+        $this->hostIndex = $hostIndex;
     }
 
     /**
      * Get the host index
      *
-     * @return Host index
+     * @return int Host index
      */
     public function getHostIndex()
     {
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/ApiException.php b/samples/client/petstore/php/OpenAPIClient-php/lib/ApiException.php
index f041f3e77239..db8899ae4e73 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/ApiException.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/ApiException.php
@@ -44,7 +44,7 @@ class ApiException extends Exception
     /**
      * The HTTP body of the server response either as Json or string.
      *
-     * @var mixed
+     * @var \stdClass|string|null
      */
     protected $responseBody;
 
@@ -58,17 +58,17 @@ class ApiException extends Exception
     /**
      * The deserialized response object
      *
-     * @var $responseObject;
+     * @var \stdClass|string|null
      */
     protected $responseObject;
 
     /**
      * Constructor
      *
-     * @param string        $message         Error message
-     * @param int           $code            HTTP status code
-     * @param string[]|null $responseHeaders HTTP response header
-     * @param mixed         $responseBody    HTTP decoded body of the server response either as \stdClass or string
+     * @param string                $message         Error message
+     * @param int                   $code            HTTP status code
+     * @param string[]|null         $responseHeaders HTTP response header
+     * @param \stdClass|string|null $responseBody    HTTP decoded body of the server response either as \stdClass or string
      */
     public function __construct($message = "", $code = 0, $responseHeaders = [], $responseBody = null)
     {
@@ -90,7 +90,7 @@ public function getResponseHeaders()
     /**
      * Gets the HTTP body of the server response either as Json or string
      *
-     * @return mixed HTTP body of the server response either as \stdClass or string
+     * @return \stdClass|string|null HTTP body of the server response either as \stdClass or string
      */
     public function getResponseBody()
     {
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Configuration.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Configuration.php
index 3ab5eda04ec4..beeafcb0dac9 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Configuration.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Configuration.php
@@ -39,6 +39,9 @@
  */
 class Configuration
 {
+    /**
+     * @var Configuration
+     */
     private static $defaultConfiguration;
 
     /**
@@ -138,7 +141,7 @@ public function setApiKey($apiKeyIdentifier, $key)
      *
      * @param string $apiKeyIdentifier API key identifier (authentication scheme)
      *
-     * @return string API key or token
+     * @return null|string API key or token
      */
     public function getApiKey($apiKeyIdentifier)
     {
@@ -164,7 +167,7 @@ public function setApiKeyPrefix($apiKeyIdentifier, $prefix)
      *
      * @param string $apiKeyIdentifier API key identifier (authentication scheme)
      *
-     * @return string
+     * @return null|string
      */
     public function getApiKeyPrefix($apiKeyIdentifier)
     {
@@ -407,7 +410,7 @@ public static function toDebugReport()
      *
      * @param  string $apiKeyIdentifier name of apikey
      *
-     * @return string API key with the prefix
+     * @return null|string API key with the prefix
      */
     public function getApiKeyWithPrefix($apiKeyIdentifier)
     {
@@ -430,7 +433,7 @@ public function getApiKeyWithPrefix($apiKeyIdentifier)
     /**
      * Returns an array of host settings
      *
-     * @return an array of host settings
+     * @return array an array of host settings
      */
     public function getHostSettings()
     {
@@ -478,9 +481,9 @@ public function getHostSettings()
     /**
      * Returns URL based on the index and variables
      *
-     * @param index array index of the host settings
-     * @param variables hash of variable and the corresponding value (optional)
-     * @return URL based on host settings
+     * @param int        $index     index of the host settings
+     * @param array|null $variables hash of variable and the corresponding value (optional)
+     * @return string URL based on host settings
      */
     public function getHostFromSettings($index, $variables = null)
     {
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/HeaderSelector.php b/samples/client/petstore/php/OpenAPIClient-php/lib/HeaderSelector.php
index 25a92414028b..eca0ee2693fe 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/HeaderSelector.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/HeaderSelector.php
@@ -76,7 +76,7 @@ public function selectHeadersForMultipart($accept)
      *
      * @param string[] $accept Array of header
      *
-     * @return string Accept (e.g. application/json)
+     * @return null|string Accept (e.g. application/json)
      */
     private function selectAcceptHeader($accept)
     {
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/AdditionalPropertiesClass.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/AdditionalPropertiesClass.php
index 2811e834099b..023ecf32ec26 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/AdditionalPropertiesClass.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/AdditionalPropertiesClass.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class AdditionalPropertiesClass implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -65,6 +68,8 @@ class AdditionalPropertiesClass implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'map_property' => null,
@@ -182,8 +187,8 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['map_property'] = isset($data['map_property']) ? $data['map_property'] : null;
-        $this->container['map_of_map_property'] = isset($data['map_of_map_property']) ? $data['map_of_map_property'] : null;
+        $this->container['map_property'] = $data['map_property'] ?? null;
+        $this->container['map_of_map_property'] = $data['map_of_map_property'] ?? null;
     }
 
     /**
@@ -225,7 +230,7 @@ public function getMapProperty()
      *
      * @param map[string,string]|null $map_property map_property
      *
-     * @return $this
+     * @return self
      */
     public function setMapProperty($map_property)
     {
@@ -249,7 +254,7 @@ public function getMapOfMapProperty()
      *
      * @param map[string,map[string,string]]|null $map_of_map_property map_of_map_property
      *
-     * @return $this
+     * @return self
      */
     public function setMapOfMapProperty($map_of_map_property)
     {
@@ -274,18 +279,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Animal.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Animal.php
index 145ecc65ac0f..aad9487cc945 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Animal.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Animal.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class Animal implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = 'class_name';
+    public const DISCRIMINATOR = 'class_name';
 
     /**
       * The original name of the model.
@@ -65,6 +68,8 @@ class Animal implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'class_name' => null,
@@ -182,8 +187,8 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['class_name'] = isset($data['class_name']) ? $data['class_name'] : null;
-        $this->container['color'] = isset($data['color']) ? $data['color'] : 'red';
+        $this->container['class_name'] = $data['class_name'] ?? null;
+        $this->container['color'] = $data['color'] ?? 'red';
 
         // Initialize discriminator property with the model name.
         $this->container['class_name'] = static::$openAPIModelName;
@@ -231,7 +236,7 @@ public function getClassName()
      *
      * @param string $class_name class_name
      *
-     * @return $this
+     * @return self
      */
     public function setClassName($class_name)
     {
@@ -255,7 +260,7 @@ public function getColor()
      *
      * @param string|null $color color
      *
-     * @return $this
+     * @return self
      */
     public function setColor($color)
     {
@@ -280,18 +285,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ApiResponse.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ApiResponse.php
index 43244c474eea..d21fa35621f5 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ApiResponse.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ApiResponse.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class ApiResponse implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -66,6 +69,8 @@ class ApiResponse implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'code' => 'int32',
@@ -187,9 +192,9 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['code'] = isset($data['code']) ? $data['code'] : null;
-        $this->container['type'] = isset($data['type']) ? $data['type'] : null;
-        $this->container['message'] = isset($data['message']) ? $data['message'] : null;
+        $this->container['code'] = $data['code'] ?? null;
+        $this->container['type'] = $data['type'] ?? null;
+        $this->container['message'] = $data['message'] ?? null;
     }
 
     /**
@@ -231,7 +236,7 @@ public function getCode()
      *
      * @param int|null $code code
      *
-     * @return $this
+     * @return self
      */
     public function setCode($code)
     {
@@ -255,7 +260,7 @@ public function getType()
      *
      * @param string|null $type type
      *
-     * @return $this
+     * @return self
      */
     public function setType($type)
     {
@@ -279,7 +284,7 @@ public function getMessage()
      *
      * @param string|null $message message
      *
-     * @return $this
+     * @return self
      */
     public function setMessage($message)
     {
@@ -304,18 +309,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayOfArrayOfNumberOnly.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayOfArrayOfNumberOnly.php
index a0f5ccfd05a7..4deeb067f680 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayOfArrayOfNumberOnly.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayOfArrayOfNumberOnly.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class ArrayOfArrayOfNumberOnly implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -64,6 +67,8 @@ class ArrayOfArrayOfNumberOnly implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'array_array_number' => null
@@ -177,7 +182,7 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['array_array_number'] = isset($data['array_array_number']) ? $data['array_array_number'] : null;
+        $this->container['array_array_number'] = $data['array_array_number'] ?? null;
     }
 
     /**
@@ -219,7 +224,7 @@ public function getArrayArrayNumber()
      *
      * @param float[][]|null $array_array_number array_array_number
      *
-     * @return $this
+     * @return self
      */
     public function setArrayArrayNumber($array_array_number)
     {
@@ -244,18 +249,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayOfNumberOnly.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayOfNumberOnly.php
index 483ea4fbd9e7..cf6fe89d16e6 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayOfNumberOnly.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayOfNumberOnly.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class ArrayOfNumberOnly implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -64,6 +67,8 @@ class ArrayOfNumberOnly implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'array_number' => null
@@ -177,7 +182,7 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['array_number'] = isset($data['array_number']) ? $data['array_number'] : null;
+        $this->container['array_number'] = $data['array_number'] ?? null;
     }
 
     /**
@@ -219,7 +224,7 @@ public function getArrayNumber()
      *
      * @param float[]|null $array_number array_number
      *
-     * @return $this
+     * @return self
      */
     public function setArrayNumber($array_number)
     {
@@ -244,18 +249,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayTest.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayTest.php
index bad6739097d4..7f598ae04fa7 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayTest.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayTest.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class ArrayTest implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -66,6 +69,8 @@ class ArrayTest implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'array_of_string' => null,
@@ -187,9 +192,9 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['array_of_string'] = isset($data['array_of_string']) ? $data['array_of_string'] : null;
-        $this->container['array_array_of_integer'] = isset($data['array_array_of_integer']) ? $data['array_array_of_integer'] : null;
-        $this->container['array_array_of_model'] = isset($data['array_array_of_model']) ? $data['array_array_of_model'] : null;
+        $this->container['array_of_string'] = $data['array_of_string'] ?? null;
+        $this->container['array_array_of_integer'] = $data['array_array_of_integer'] ?? null;
+        $this->container['array_array_of_model'] = $data['array_array_of_model'] ?? null;
     }
 
     /**
@@ -231,7 +236,7 @@ public function getArrayOfString()
      *
      * @param string[]|null $array_of_string array_of_string
      *
-     * @return $this
+     * @return self
      */
     public function setArrayOfString($array_of_string)
     {
@@ -255,7 +260,7 @@ public function getArrayArrayOfInteger()
      *
      * @param int[][]|null $array_array_of_integer array_array_of_integer
      *
-     * @return $this
+     * @return self
      */
     public function setArrayArrayOfInteger($array_array_of_integer)
     {
@@ -279,7 +284,7 @@ public function getArrayArrayOfModel()
      *
      * @param \OpenAPI\Client\Model\ReadOnlyFirst[][]|null $array_array_of_model array_array_of_model
      *
-     * @return $this
+     * @return self
      */
     public function setArrayArrayOfModel($array_array_of_model)
     {
@@ -304,18 +309,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Capitalization.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Capitalization.php
index 973de7be8fce..5fa154bee4ad 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Capitalization.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Capitalization.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class Capitalization implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -69,6 +72,8 @@ class Capitalization implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'small_camel' => null,
@@ -202,12 +207,12 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['small_camel'] = isset($data['small_camel']) ? $data['small_camel'] : null;
-        $this->container['capital_camel'] = isset($data['capital_camel']) ? $data['capital_camel'] : null;
-        $this->container['small_snake'] = isset($data['small_snake']) ? $data['small_snake'] : null;
-        $this->container['capital_snake'] = isset($data['capital_snake']) ? $data['capital_snake'] : null;
-        $this->container['sca_eth_flow_points'] = isset($data['sca_eth_flow_points']) ? $data['sca_eth_flow_points'] : null;
-        $this->container['att_name'] = isset($data['att_name']) ? $data['att_name'] : null;
+        $this->container['small_camel'] = $data['small_camel'] ?? null;
+        $this->container['capital_camel'] = $data['capital_camel'] ?? null;
+        $this->container['small_snake'] = $data['small_snake'] ?? null;
+        $this->container['capital_snake'] = $data['capital_snake'] ?? null;
+        $this->container['sca_eth_flow_points'] = $data['sca_eth_flow_points'] ?? null;
+        $this->container['att_name'] = $data['att_name'] ?? null;
     }
 
     /**
@@ -249,7 +254,7 @@ public function getSmallCamel()
      *
      * @param string|null $small_camel small_camel
      *
-     * @return $this
+     * @return self
      */
     public function setSmallCamel($small_camel)
     {
@@ -273,7 +278,7 @@ public function getCapitalCamel()
      *
      * @param string|null $capital_camel capital_camel
      *
-     * @return $this
+     * @return self
      */
     public function setCapitalCamel($capital_camel)
     {
@@ -297,7 +302,7 @@ public function getSmallSnake()
      *
      * @param string|null $small_snake small_snake
      *
-     * @return $this
+     * @return self
      */
     public function setSmallSnake($small_snake)
     {
@@ -321,7 +326,7 @@ public function getCapitalSnake()
      *
      * @param string|null $capital_snake capital_snake
      *
-     * @return $this
+     * @return self
      */
     public function setCapitalSnake($capital_snake)
     {
@@ -345,7 +350,7 @@ public function getScaEthFlowPoints()
      *
      * @param string|null $sca_eth_flow_points sca_eth_flow_points
      *
-     * @return $this
+     * @return self
      */
     public function setScaEthFlowPoints($sca_eth_flow_points)
     {
@@ -369,7 +374,7 @@ public function getAttName()
      *
      * @param string|null $att_name Name of the pet
      *
-     * @return $this
+     * @return self
      */
     public function setAttName($att_name)
     {
@@ -394,18 +399,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Cat.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Cat.php
index 5603aab4c7df..75e10661e9fc 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Cat.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Cat.php
@@ -37,10 +37,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class Cat extends Animal 
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -62,6 +65,8 @@ class Cat extends Animal
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'declawed' => null
@@ -171,7 +176,7 @@ public function __construct(array $data = null)
     {
         parent::__construct($data);
 
-        $this->container['declawed'] = isset($data['declawed']) ? $data['declawed'] : null;
+        $this->container['declawed'] = $data['declawed'] ?? null;
     }
 
     /**
@@ -213,7 +218,7 @@ public function getDeclawed()
      *
      * @param bool|null $declawed declawed
      *
-     * @return $this
+     * @return self
      */
     public function setDeclawed($declawed)
     {
@@ -238,18 +243,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/CatAllOf.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/CatAllOf.php
index 8d31dffa0f55..d40c515390f7 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/CatAllOf.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/CatAllOf.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class CatAllOf implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -64,6 +67,8 @@ class CatAllOf implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'declawed' => null
@@ -177,7 +182,7 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['declawed'] = isset($data['declawed']) ? $data['declawed'] : null;
+        $this->container['declawed'] = $data['declawed'] ?? null;
     }
 
     /**
@@ -219,7 +224,7 @@ public function getDeclawed()
      *
      * @param bool|null $declawed declawed
      *
-     * @return $this
+     * @return self
      */
     public function setDeclawed($declawed)
     {
@@ -244,18 +249,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Category.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Category.php
index 174fdd9b84f1..6137a3246008 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Category.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Category.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class Category implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -65,6 +68,8 @@ class Category implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'id' => 'int64',
@@ -182,8 +187,8 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['id'] = isset($data['id']) ? $data['id'] : null;
-        $this->container['name'] = isset($data['name']) ? $data['name'] : 'default-name';
+        $this->container['id'] = $data['id'] ?? null;
+        $this->container['name'] = $data['name'] ?? 'default-name';
     }
 
     /**
@@ -228,7 +233,7 @@ public function getId()
      *
      * @param int|null $id id
      *
-     * @return $this
+     * @return self
      */
     public function setId($id)
     {
@@ -252,7 +257,7 @@ public function getName()
      *
      * @param string $name name
      *
-     * @return $this
+     * @return self
      */
     public function setName($name)
     {
@@ -277,18 +282,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ClassModel.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ClassModel.php
index f833dea74f39..9754dc5466c9 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ClassModel.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ClassModel.php
@@ -40,10 +40,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class ClassModel implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -65,6 +68,8 @@ class ClassModel implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         '_class' => null
@@ -178,7 +183,7 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['_class'] = isset($data['_class']) ? $data['_class'] : null;
+        $this->container['_class'] = $data['_class'] ?? null;
     }
 
     /**
@@ -220,7 +225,7 @@ public function getClass()
      *
      * @param string|null $_class _class
      *
-     * @return $this
+     * @return self
      */
     public function setClass($_class)
     {
@@ -245,18 +250,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Client.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Client.php
index 564b89cec449..8099e47db035 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Client.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Client.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class Client implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -64,6 +67,8 @@ class Client implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'client' => null
@@ -177,7 +182,7 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['client'] = isset($data['client']) ? $data['client'] : null;
+        $this->container['client'] = $data['client'] ?? null;
     }
 
     /**
@@ -219,7 +224,7 @@ public function getClient()
      *
      * @param string|null $client client
      *
-     * @return $this
+     * @return self
      */
     public function setClient($client)
     {
@@ -244,18 +249,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Dog.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Dog.php
index 4a205e6a0acd..8e60b41c02c0 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Dog.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Dog.php
@@ -37,10 +37,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class Dog extends Animal 
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -62,6 +65,8 @@ class Dog extends Animal
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'breed' => null
@@ -171,7 +176,7 @@ public function __construct(array $data = null)
     {
         parent::__construct($data);
 
-        $this->container['breed'] = isset($data['breed']) ? $data['breed'] : null;
+        $this->container['breed'] = $data['breed'] ?? null;
     }
 
     /**
@@ -213,7 +218,7 @@ public function getBreed()
      *
      * @param string|null $breed breed
      *
-     * @return $this
+     * @return self
      */
     public function setBreed($breed)
     {
@@ -238,18 +243,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/DogAllOf.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/DogAllOf.php
index dc8ac5fefe7f..d6edf67ccee2 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/DogAllOf.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/DogAllOf.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class DogAllOf implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -64,6 +67,8 @@ class DogAllOf implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'breed' => null
@@ -177,7 +182,7 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['breed'] = isset($data['breed']) ? $data['breed'] : null;
+        $this->container['breed'] = $data['breed'] ?? null;
     }
 
     /**
@@ -219,7 +224,7 @@ public function getBreed()
      *
      * @param string|null $breed breed
      *
-     * @return $this
+     * @return self
      */
     public function setBreed($breed)
     {
@@ -244,18 +249,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/EnumArrays.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/EnumArrays.php
index b26906a75cc4..ed05ebfacf75 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/EnumArrays.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/EnumArrays.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class EnumArrays implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -65,6 +68,8 @@ class EnumArrays implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'just_symbol' => null,
@@ -212,8 +217,8 @@ public function getArrayEnumAllowableValues()
      */
     public function __construct(array $data = null)
     {
-        $this->container['just_symbol'] = isset($data['just_symbol']) ? $data['just_symbol'] : null;
-        $this->container['array_enum'] = isset($data['array_enum']) ? $data['array_enum'] : null;
+        $this->container['just_symbol'] = $data['just_symbol'] ?? null;
+        $this->container['array_enum'] = $data['array_enum'] ?? null;
     }
 
     /**
@@ -263,7 +268,7 @@ public function getJustSymbol()
      *
      * @param string|null $just_symbol just_symbol
      *
-     * @return $this
+     * @return self
      */
     public function setJustSymbol($just_symbol)
     {
@@ -296,7 +301,7 @@ public function getArrayEnum()
      *
      * @param string[]|null $array_enum array_enum
      *
-     * @return $this
+     * @return self
      */
     public function setArrayEnum($array_enum)
     {
@@ -330,18 +335,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/EnumTest.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/EnumTest.php
index 005a3fea0b3c..8d4bd318cee9 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/EnumTest.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/EnumTest.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class EnumTest implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -71,6 +74,8 @@ class EnumTest implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'enum_string' => null,
@@ -276,14 +281,14 @@ public function getEnumNumberAllowableValues()
      */
     public function __construct(array $data = null)
     {
-        $this->container['enum_string'] = isset($data['enum_string']) ? $data['enum_string'] : null;
-        $this->container['enum_string_required'] = isset($data['enum_string_required']) ? $data['enum_string_required'] : null;
-        $this->container['enum_integer'] = isset($data['enum_integer']) ? $data['enum_integer'] : null;
-        $this->container['enum_number'] = isset($data['enum_number']) ? $data['enum_number'] : null;
-        $this->container['outer_enum'] = isset($data['outer_enum']) ? $data['outer_enum'] : null;
-        $this->container['outer_enum_integer'] = isset($data['outer_enum_integer']) ? $data['outer_enum_integer'] : null;
-        $this->container['outer_enum_default_value'] = isset($data['outer_enum_default_value']) ? $data['outer_enum_default_value'] : null;
-        $this->container['outer_enum_integer_default_value'] = isset($data['outer_enum_integer_default_value']) ? $data['outer_enum_integer_default_value'] : null;
+        $this->container['enum_string'] = $data['enum_string'] ?? null;
+        $this->container['enum_string_required'] = $data['enum_string_required'] ?? null;
+        $this->container['enum_integer'] = $data['enum_integer'] ?? null;
+        $this->container['enum_number'] = $data['enum_number'] ?? null;
+        $this->container['outer_enum'] = $data['outer_enum'] ?? null;
+        $this->container['outer_enum_integer'] = $data['outer_enum_integer'] ?? null;
+        $this->container['outer_enum_default_value'] = $data['outer_enum_default_value'] ?? null;
+        $this->container['outer_enum_integer_default_value'] = $data['outer_enum_integer_default_value'] ?? null;
     }
 
     /**
@@ -360,7 +365,7 @@ public function getEnumString()
      *
      * @param string|null $enum_string enum_string
      *
-     * @return $this
+     * @return self
      */
     public function setEnumString($enum_string)
     {
@@ -393,7 +398,7 @@ public function getEnumStringRequired()
      *
      * @param string $enum_string_required enum_string_required
      *
-     * @return $this
+     * @return self
      */
     public function setEnumStringRequired($enum_string_required)
     {
@@ -426,7 +431,7 @@ public function getEnumInteger()
      *
      * @param int|null $enum_integer enum_integer
      *
-     * @return $this
+     * @return self
      */
     public function setEnumInteger($enum_integer)
     {
@@ -459,7 +464,7 @@ public function getEnumNumber()
      *
      * @param double|null $enum_number enum_number
      *
-     * @return $this
+     * @return self
      */
     public function setEnumNumber($enum_number)
     {
@@ -492,7 +497,7 @@ public function getOuterEnum()
      *
      * @param \OpenAPI\Client\Model\OuterEnum|null $outer_enum outer_enum
      *
-     * @return $this
+     * @return self
      */
     public function setOuterEnum($outer_enum)
     {
@@ -516,7 +521,7 @@ public function getOuterEnumInteger()
      *
      * @param \OpenAPI\Client\Model\OuterEnumInteger|null $outer_enum_integer outer_enum_integer
      *
-     * @return $this
+     * @return self
      */
     public function setOuterEnumInteger($outer_enum_integer)
     {
@@ -540,7 +545,7 @@ public function getOuterEnumDefaultValue()
      *
      * @param \OpenAPI\Client\Model\OuterEnumDefaultValue|null $outer_enum_default_value outer_enum_default_value
      *
-     * @return $this
+     * @return self
      */
     public function setOuterEnumDefaultValue($outer_enum_default_value)
     {
@@ -564,7 +569,7 @@ public function getOuterEnumIntegerDefaultValue()
      *
      * @param \OpenAPI\Client\Model\OuterEnumIntegerDefaultValue|null $outer_enum_integer_default_value outer_enum_integer_default_value
      *
-     * @return $this
+     * @return self
      */
     public function setOuterEnumIntegerDefaultValue($outer_enum_integer_default_value)
     {
@@ -589,18 +594,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/File.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/File.php
index 03a15d5b8021..cb0a923af33b 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/File.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/File.php
@@ -40,10 +40,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class File implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -65,6 +68,8 @@ class File implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'source_uri' => null
@@ -178,7 +183,7 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['source_uri'] = isset($data['source_uri']) ? $data['source_uri'] : null;
+        $this->container['source_uri'] = $data['source_uri'] ?? null;
     }
 
     /**
@@ -220,7 +225,7 @@ public function getSourceUri()
      *
      * @param string|null $source_uri Test capitalization
      *
-     * @return $this
+     * @return self
      */
     public function setSourceUri($source_uri)
     {
@@ -245,18 +250,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FileSchemaTestClass.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FileSchemaTestClass.php
index 4f8ffd8d9de8..165c679fdc3f 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FileSchemaTestClass.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FileSchemaTestClass.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class FileSchemaTestClass implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -65,6 +68,8 @@ class FileSchemaTestClass implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'file' => null,
@@ -182,8 +187,8 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['file'] = isset($data['file']) ? $data['file'] : null;
-        $this->container['files'] = isset($data['files']) ? $data['files'] : null;
+        $this->container['file'] = $data['file'] ?? null;
+        $this->container['files'] = $data['files'] ?? null;
     }
 
     /**
@@ -225,7 +230,7 @@ public function getFile()
      *
      * @param \OpenAPI\Client\Model\File|null $file file
      *
-     * @return $this
+     * @return self
      */
     public function setFile($file)
     {
@@ -249,7 +254,7 @@ public function getFiles()
      *
      * @param \OpenAPI\Client\Model\File[]|null $files files
      *
-     * @return $this
+     * @return self
      */
     public function setFiles($files)
     {
@@ -274,18 +279,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Foo.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Foo.php
index 8213f1d0e348..b7562e157007 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Foo.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Foo.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class Foo implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -64,6 +67,8 @@ class Foo implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'bar' => null
@@ -177,7 +182,7 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['bar'] = isset($data['bar']) ? $data['bar'] : 'bar';
+        $this->container['bar'] = $data['bar'] ?? 'bar';
     }
 
     /**
@@ -219,7 +224,7 @@ public function getBar()
      *
      * @param string|null $bar bar
      *
-     * @return $this
+     * @return self
      */
     public function setBar($bar)
     {
@@ -244,18 +249,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FormatTest.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FormatTest.php
index 0394d187aca0..49b33571f0ca 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FormatTest.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FormatTest.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class FormatTest implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -78,6 +81,8 @@ class FormatTest implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'integer' => null,
@@ -247,21 +252,21 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['integer'] = isset($data['integer']) ? $data['integer'] : null;
-        $this->container['int32'] = isset($data['int32']) ? $data['int32'] : null;
-        $this->container['int64'] = isset($data['int64']) ? $data['int64'] : null;
-        $this->container['number'] = isset($data['number']) ? $data['number'] : null;
-        $this->container['float'] = isset($data['float']) ? $data['float'] : null;
-        $this->container['double'] = isset($data['double']) ? $data['double'] : null;
-        $this->container['string'] = isset($data['string']) ? $data['string'] : null;
-        $this->container['byte'] = isset($data['byte']) ? $data['byte'] : null;
-        $this->container['binary'] = isset($data['binary']) ? $data['binary'] : null;
-        $this->container['date'] = isset($data['date']) ? $data['date'] : null;
-        $this->container['date_time'] = isset($data['date_time']) ? $data['date_time'] : null;
-        $this->container['uuid'] = isset($data['uuid']) ? $data['uuid'] : null;
-        $this->container['password'] = isset($data['password']) ? $data['password'] : null;
-        $this->container['pattern_with_digits'] = isset($data['pattern_with_digits']) ? $data['pattern_with_digits'] : null;
-        $this->container['pattern_with_digits_and_delimiter'] = isset($data['pattern_with_digits_and_delimiter']) ? $data['pattern_with_digits_and_delimiter'] : null;
+        $this->container['integer'] = $data['integer'] ?? null;
+        $this->container['int32'] = $data['int32'] ?? null;
+        $this->container['int64'] = $data['int64'] ?? null;
+        $this->container['number'] = $data['number'] ?? null;
+        $this->container['float'] = $data['float'] ?? null;
+        $this->container['double'] = $data['double'] ?? null;
+        $this->container['string'] = $data['string'] ?? null;
+        $this->container['byte'] = $data['byte'] ?? null;
+        $this->container['binary'] = $data['binary'] ?? null;
+        $this->container['date'] = $data['date'] ?? null;
+        $this->container['date_time'] = $data['date_time'] ?? null;
+        $this->container['uuid'] = $data['uuid'] ?? null;
+        $this->container['password'] = $data['password'] ?? null;
+        $this->container['pattern_with_digits'] = $data['pattern_with_digits'] ?? null;
+        $this->container['pattern_with_digits_and_delimiter'] = $data['pattern_with_digits_and_delimiter'] ?? null;
     }
 
     /**
@@ -375,7 +380,7 @@ public function getInteger()
      *
      * @param int|null $integer integer
      *
-     * @return $this
+     * @return self
      */
     public function setInteger($integer)
     {
@@ -407,7 +412,7 @@ public function getInt32()
      *
      * @param int|null $int32 int32
      *
-     * @return $this
+     * @return self
      */
     public function setInt32($int32)
     {
@@ -439,7 +444,7 @@ public function getInt64()
      *
      * @param int|null $int64 int64
      *
-     * @return $this
+     * @return self
      */
     public function setInt64($int64)
     {
@@ -463,7 +468,7 @@ public function getNumber()
      *
      * @param float $number number
      *
-     * @return $this
+     * @return self
      */
     public function setNumber($number)
     {
@@ -495,7 +500,7 @@ public function getFloat()
      *
      * @param float|null $float float
      *
-     * @return $this
+     * @return self
      */
     public function setFloat($float)
     {
@@ -527,7 +532,7 @@ public function getDouble()
      *
      * @param double|null $double double
      *
-     * @return $this
+     * @return self
      */
     public function setDouble($double)
     {
@@ -559,7 +564,7 @@ public function getString()
      *
      * @param string|null $string string
      *
-     * @return $this
+     * @return self
      */
     public function setString($string)
     {
@@ -588,7 +593,7 @@ public function getByte()
      *
      * @param string $byte byte
      *
-     * @return $this
+     * @return self
      */
     public function setByte($byte)
     {
@@ -612,7 +617,7 @@ public function getBinary()
      *
      * @param \SplFileObject|null $binary binary
      *
-     * @return $this
+     * @return self
      */
     public function setBinary($binary)
     {
@@ -636,7 +641,7 @@ public function getDate()
      *
      * @param \DateTime $date date
      *
-     * @return $this
+     * @return self
      */
     public function setDate($date)
     {
@@ -660,7 +665,7 @@ public function getDateTime()
      *
      * @param \DateTime|null $date_time date_time
      *
-     * @return $this
+     * @return self
      */
     public function setDateTime($date_time)
     {
@@ -684,7 +689,7 @@ public function getUuid()
      *
      * @param string|null $uuid uuid
      *
-     * @return $this
+     * @return self
      */
     public function setUuid($uuid)
     {
@@ -708,7 +713,7 @@ public function getPassword()
      *
      * @param string $password password
      *
-     * @return $this
+     * @return self
      */
     public function setPassword($password)
     {
@@ -739,7 +744,7 @@ public function getPatternWithDigits()
      *
      * @param string|null $pattern_with_digits A string that is a 10 digit number. Can have leading zeros.
      *
-     * @return $this
+     * @return self
      */
     public function setPatternWithDigits($pattern_with_digits)
     {
@@ -768,7 +773,7 @@ public function getPatternWithDigitsAndDelimiter()
      *
      * @param string|null $pattern_with_digits_and_delimiter A string starting with 'image_' (case insensitive) and one to three digits following i.e. Image_01.
      *
-     * @return $this
+     * @return self
      */
     public function setPatternWithDigitsAndDelimiter($pattern_with_digits_and_delimiter)
     {
@@ -798,18 +803,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/HasOnlyReadOnly.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/HasOnlyReadOnly.php
index 40a8e5584fc3..eb7571b26510 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/HasOnlyReadOnly.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/HasOnlyReadOnly.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class HasOnlyReadOnly implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -65,6 +68,8 @@ class HasOnlyReadOnly implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'bar' => null,
@@ -182,8 +187,8 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['bar'] = isset($data['bar']) ? $data['bar'] : null;
-        $this->container['foo'] = isset($data['foo']) ? $data['foo'] : null;
+        $this->container['bar'] = $data['bar'] ?? null;
+        $this->container['foo'] = $data['foo'] ?? null;
     }
 
     /**
@@ -225,7 +230,7 @@ public function getBar()
      *
      * @param string|null $bar bar
      *
-     * @return $this
+     * @return self
      */
     public function setBar($bar)
     {
@@ -249,7 +254,7 @@ public function getFoo()
      *
      * @param string|null $foo foo
      *
-     * @return $this
+     * @return self
      */
     public function setFoo($foo)
     {
@@ -274,18 +279,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/HealthCheckResult.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/HealthCheckResult.php
index 1f959f71635f..ec6b27724c85 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/HealthCheckResult.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/HealthCheckResult.php
@@ -40,10 +40,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class HealthCheckResult implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -65,6 +68,8 @@ class HealthCheckResult implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'nullable_message' => null
@@ -178,7 +183,7 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['nullable_message'] = isset($data['nullable_message']) ? $data['nullable_message'] : null;
+        $this->container['nullable_message'] = $data['nullable_message'] ?? null;
     }
 
     /**
@@ -220,7 +225,7 @@ public function getNullableMessage()
      *
      * @param string|null $nullable_message nullable_message
      *
-     * @return $this
+     * @return self
      */
     public function setNullableMessage($nullable_message)
     {
@@ -245,18 +250,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject.php
index 17808cab18ec..05aed891fbba 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class InlineObject implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -65,6 +68,8 @@ class InlineObject implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'name' => null,
@@ -182,8 +187,8 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['name'] = isset($data['name']) ? $data['name'] : null;
-        $this->container['status'] = isset($data['status']) ? $data['status'] : null;
+        $this->container['name'] = $data['name'] ?? null;
+        $this->container['status'] = $data['status'] ?? null;
     }
 
     /**
@@ -225,7 +230,7 @@ public function getName()
      *
      * @param string|null $name Updated name of the pet
      *
-     * @return $this
+     * @return self
      */
     public function setName($name)
     {
@@ -249,7 +254,7 @@ public function getStatus()
      *
      * @param string|null $status Updated status of the pet
      *
-     * @return $this
+     * @return self
      */
     public function setStatus($status)
     {
@@ -274,18 +279,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject1.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject1.php
index 7c16738bc07b..a1dbbb404ab5 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject1.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject1.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class InlineObject1 implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -65,6 +68,8 @@ class InlineObject1 implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'additional_metadata' => null,
@@ -182,8 +187,8 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['additional_metadata'] = isset($data['additional_metadata']) ? $data['additional_metadata'] : null;
-        $this->container['file'] = isset($data['file']) ? $data['file'] : null;
+        $this->container['additional_metadata'] = $data['additional_metadata'] ?? null;
+        $this->container['file'] = $data['file'] ?? null;
     }
 
     /**
@@ -225,7 +230,7 @@ public function getAdditionalMetadata()
      *
      * @param string|null $additional_metadata Additional data to pass to server
      *
-     * @return $this
+     * @return self
      */
     public function setAdditionalMetadata($additional_metadata)
     {
@@ -249,7 +254,7 @@ public function getFile()
      *
      * @param \SplFileObject|null $file file to upload
      *
-     * @return $this
+     * @return self
      */
     public function setFile($file)
     {
@@ -274,18 +279,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject2.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject2.php
index 5459e3475bca..d5849b237440 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject2.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject2.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class InlineObject2 implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -65,6 +68,8 @@ class InlineObject2 implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'enum_form_string_array' => null,
@@ -214,8 +219,8 @@ public function getEnumFormStringAllowableValues()
      */
     public function __construct(array $data = null)
     {
-        $this->container['enum_form_string_array'] = isset($data['enum_form_string_array']) ? $data['enum_form_string_array'] : null;
-        $this->container['enum_form_string'] = isset($data['enum_form_string']) ? $data['enum_form_string'] : '-efg';
+        $this->container['enum_form_string_array'] = $data['enum_form_string_array'] ?? null;
+        $this->container['enum_form_string'] = $data['enum_form_string'] ?? '-efg';
     }
 
     /**
@@ -265,7 +270,7 @@ public function getEnumFormStringArray()
      *
      * @param string[]|null $enum_form_string_array Form parameter enum test (string array)
      *
-     * @return $this
+     * @return self
      */
     public function setEnumFormStringArray($enum_form_string_array)
     {
@@ -298,7 +303,7 @@ public function getEnumFormString()
      *
      * @param string|null $enum_form_string Form parameter enum test (string)
      *
-     * @return $this
+     * @return self
      */
     public function setEnumFormString($enum_form_string)
     {
@@ -332,18 +337,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject3.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject3.php
index c1383f808038..4fa7ba14dd78 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject3.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject3.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class InlineObject3 implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -77,6 +80,8 @@ class InlineObject3 implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'integer' => null,
@@ -242,20 +247,20 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['integer'] = isset($data['integer']) ? $data['integer'] : null;
-        $this->container['int32'] = isset($data['int32']) ? $data['int32'] : null;
-        $this->container['int64'] = isset($data['int64']) ? $data['int64'] : null;
-        $this->container['number'] = isset($data['number']) ? $data['number'] : null;
-        $this->container['float'] = isset($data['float']) ? $data['float'] : null;
-        $this->container['double'] = isset($data['double']) ? $data['double'] : null;
-        $this->container['string'] = isset($data['string']) ? $data['string'] : null;
-        $this->container['pattern_without_delimiter'] = isset($data['pattern_without_delimiter']) ? $data['pattern_without_delimiter'] : null;
-        $this->container['byte'] = isset($data['byte']) ? $data['byte'] : null;
-        $this->container['binary'] = isset($data['binary']) ? $data['binary'] : null;
-        $this->container['date'] = isset($data['date']) ? $data['date'] : null;
-        $this->container['date_time'] = isset($data['date_time']) ? $data['date_time'] : null;
-        $this->container['password'] = isset($data['password']) ? $data['password'] : null;
-        $this->container['callback'] = isset($data['callback']) ? $data['callback'] : null;
+        $this->container['integer'] = $data['integer'] ?? null;
+        $this->container['int32'] = $data['int32'] ?? null;
+        $this->container['int64'] = $data['int64'] ?? null;
+        $this->container['number'] = $data['number'] ?? null;
+        $this->container['float'] = $data['float'] ?? null;
+        $this->container['double'] = $data['double'] ?? null;
+        $this->container['string'] = $data['string'] ?? null;
+        $this->container['pattern_without_delimiter'] = $data['pattern_without_delimiter'] ?? null;
+        $this->container['byte'] = $data['byte'] ?? null;
+        $this->container['binary'] = $data['binary'] ?? null;
+        $this->container['date'] = $data['date'] ?? null;
+        $this->container['date_time'] = $data['date_time'] ?? null;
+        $this->container['password'] = $data['password'] ?? null;
+        $this->container['callback'] = $data['callback'] ?? null;
     }
 
     /**
@@ -361,7 +366,7 @@ public function getInteger()
      *
      * @param int|null $integer None
      *
-     * @return $this
+     * @return self
      */
     public function setInteger($integer)
     {
@@ -393,7 +398,7 @@ public function getInt32()
      *
      * @param int|null $int32 None
      *
-     * @return $this
+     * @return self
      */
     public function setInt32($int32)
     {
@@ -425,7 +430,7 @@ public function getInt64()
      *
      * @param int|null $int64 None
      *
-     * @return $this
+     * @return self
      */
     public function setInt64($int64)
     {
@@ -449,7 +454,7 @@ public function getNumber()
      *
      * @param float $number None
      *
-     * @return $this
+     * @return self
      */
     public function setNumber($number)
     {
@@ -481,7 +486,7 @@ public function getFloat()
      *
      * @param float|null $float None
      *
-     * @return $this
+     * @return self
      */
     public function setFloat($float)
     {
@@ -510,7 +515,7 @@ public function getDouble()
      *
      * @param double $double None
      *
-     * @return $this
+     * @return self
      */
     public function setDouble($double)
     {
@@ -542,7 +547,7 @@ public function getString()
      *
      * @param string|null $string None
      *
-     * @return $this
+     * @return self
      */
     public function setString($string)
     {
@@ -571,7 +576,7 @@ public function getPatternWithoutDelimiter()
      *
      * @param string $pattern_without_delimiter None
      *
-     * @return $this
+     * @return self
      */
     public function setPatternWithoutDelimiter($pattern_without_delimiter)
     {
@@ -600,7 +605,7 @@ public function getByte()
      *
      * @param string $byte None
      *
-     * @return $this
+     * @return self
      */
     public function setByte($byte)
     {
@@ -624,7 +629,7 @@ public function getBinary()
      *
      * @param \SplFileObject|null $binary None
      *
-     * @return $this
+     * @return self
      */
     public function setBinary($binary)
     {
@@ -648,7 +653,7 @@ public function getDate()
      *
      * @param \DateTime|null $date None
      *
-     * @return $this
+     * @return self
      */
     public function setDate($date)
     {
@@ -672,7 +677,7 @@ public function getDateTime()
      *
      * @param \DateTime|null $date_time None
      *
-     * @return $this
+     * @return self
      */
     public function setDateTime($date_time)
     {
@@ -696,7 +701,7 @@ public function getPassword()
      *
      * @param string|null $password None
      *
-     * @return $this
+     * @return self
      */
     public function setPassword($password)
     {
@@ -727,7 +732,7 @@ public function getCallback()
      *
      * @param string|null $callback None
      *
-     * @return $this
+     * @return self
      */
     public function setCallback($callback)
     {
@@ -752,18 +757,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject4.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject4.php
index 67120fcf6a47..04a9d0743434 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject4.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject4.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class InlineObject4 implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -65,6 +68,8 @@ class InlineObject4 implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'param' => null,
@@ -182,8 +187,8 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['param'] = isset($data['param']) ? $data['param'] : null;
-        $this->container['param2'] = isset($data['param2']) ? $data['param2'] : null;
+        $this->container['param'] = $data['param'] ?? null;
+        $this->container['param2'] = $data['param2'] ?? null;
     }
 
     /**
@@ -231,7 +236,7 @@ public function getParam()
      *
      * @param string $param field1
      *
-     * @return $this
+     * @return self
      */
     public function setParam($param)
     {
@@ -255,7 +260,7 @@ public function getParam2()
      *
      * @param string $param2 field2
      *
-     * @return $this
+     * @return self
      */
     public function setParam2($param2)
     {
@@ -280,18 +285,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject5.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject5.php
index fe0456b3a838..fba00cddf6a6 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject5.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineObject5.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class InlineObject5 implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -65,6 +68,8 @@ class InlineObject5 implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'additional_metadata' => null,
@@ -182,8 +187,8 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['additional_metadata'] = isset($data['additional_metadata']) ? $data['additional_metadata'] : null;
-        $this->container['required_file'] = isset($data['required_file']) ? $data['required_file'] : null;
+        $this->container['additional_metadata'] = $data['additional_metadata'] ?? null;
+        $this->container['required_file'] = $data['required_file'] ?? null;
     }
 
     /**
@@ -228,7 +233,7 @@ public function getAdditionalMetadata()
      *
      * @param string|null $additional_metadata Additional data to pass to server
      *
-     * @return $this
+     * @return self
      */
     public function setAdditionalMetadata($additional_metadata)
     {
@@ -252,7 +257,7 @@ public function getRequiredFile()
      *
      * @param \SplFileObject $required_file file to upload
      *
-     * @return $this
+     * @return self
      */
     public function setRequiredFile($required_file)
     {
@@ -277,18 +282,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineResponseDefault.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineResponseDefault.php
index 53146c15e459..b2ff1f1b8f1e 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineResponseDefault.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/InlineResponseDefault.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class InlineResponseDefault implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -64,6 +67,8 @@ class InlineResponseDefault implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'string' => null
@@ -177,7 +182,7 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['string'] = isset($data['string']) ? $data['string'] : null;
+        $this->container['string'] = $data['string'] ?? null;
     }
 
     /**
@@ -219,7 +224,7 @@ public function getString()
      *
      * @param \OpenAPI\Client\Model\Foo|null $string string
      *
-     * @return $this
+     * @return self
      */
     public function setString($string)
     {
@@ -244,18 +249,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/MapTest.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/MapTest.php
index be76b2439b92..e6f4a1294552 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/MapTest.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/MapTest.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class MapTest implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -67,6 +70,8 @@ class MapTest implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'map_map_of_string' => null,
@@ -207,10 +212,10 @@ public function getMapOfEnumStringAllowableValues()
      */
     public function __construct(array $data = null)
     {
-        $this->container['map_map_of_string'] = isset($data['map_map_of_string']) ? $data['map_map_of_string'] : null;
-        $this->container['map_of_enum_string'] = isset($data['map_of_enum_string']) ? $data['map_of_enum_string'] : null;
-        $this->container['direct_map'] = isset($data['direct_map']) ? $data['direct_map'] : null;
-        $this->container['indirect_map'] = isset($data['indirect_map']) ? $data['indirect_map'] : null;
+        $this->container['map_map_of_string'] = $data['map_map_of_string'] ?? null;
+        $this->container['map_of_enum_string'] = $data['map_of_enum_string'] ?? null;
+        $this->container['direct_map'] = $data['direct_map'] ?? null;
+        $this->container['indirect_map'] = $data['indirect_map'] ?? null;
     }
 
     /**
@@ -252,7 +257,7 @@ public function getMapMapOfString()
      *
      * @param map[string,map[string,string]]|null $map_map_of_string map_map_of_string
      *
-     * @return $this
+     * @return self
      */
     public function setMapMapOfString($map_map_of_string)
     {
@@ -276,7 +281,7 @@ public function getMapOfEnumString()
      *
      * @param map[string,string]|null $map_of_enum_string map_of_enum_string
      *
-     * @return $this
+     * @return self
      */
     public function setMapOfEnumString($map_of_enum_string)
     {
@@ -309,7 +314,7 @@ public function getDirectMap()
      *
      * @param map[string,bool]|null $direct_map direct_map
      *
-     * @return $this
+     * @return self
      */
     public function setDirectMap($direct_map)
     {
@@ -333,7 +338,7 @@ public function getIndirectMap()
      *
      * @param map[string,bool]|null $indirect_map indirect_map
      *
-     * @return $this
+     * @return self
      */
     public function setIndirectMap($indirect_map)
     {
@@ -358,18 +363,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/MixedPropertiesAndAdditionalPropertiesClass.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/MixedPropertiesAndAdditionalPropertiesClass.php
index 2522e4d5d523..31bcc81816d3 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/MixedPropertiesAndAdditionalPropertiesClass.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/MixedPropertiesAndAdditionalPropertiesClass.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class MixedPropertiesAndAdditionalPropertiesClass implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -66,6 +69,8 @@ class MixedPropertiesAndAdditionalPropertiesClass implements ModelInterface, Arr
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'uuid' => 'uuid',
@@ -187,9 +192,9 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['uuid'] = isset($data['uuid']) ? $data['uuid'] : null;
-        $this->container['date_time'] = isset($data['date_time']) ? $data['date_time'] : null;
-        $this->container['map'] = isset($data['map']) ? $data['map'] : null;
+        $this->container['uuid'] = $data['uuid'] ?? null;
+        $this->container['date_time'] = $data['date_time'] ?? null;
+        $this->container['map'] = $data['map'] ?? null;
     }
 
     /**
@@ -231,7 +236,7 @@ public function getUuid()
      *
      * @param string|null $uuid uuid
      *
-     * @return $this
+     * @return self
      */
     public function setUuid($uuid)
     {
@@ -255,7 +260,7 @@ public function getDateTime()
      *
      * @param \DateTime|null $date_time date_time
      *
-     * @return $this
+     * @return self
      */
     public function setDateTime($date_time)
     {
@@ -279,7 +284,7 @@ public function getMap()
      *
      * @param map[string,\OpenAPI\Client\Model\Animal]|null $map map
      *
-     * @return $this
+     * @return self
      */
     public function setMap($map)
     {
@@ -304,18 +309,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Model200Response.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Model200Response.php
index 5be747eb5253..92b79ab9c600 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Model200Response.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Model200Response.php
@@ -40,10 +40,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class Model200Response implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -66,6 +69,8 @@ class Model200Response implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'name' => 'int32',
@@ -183,8 +188,8 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['name'] = isset($data['name']) ? $data['name'] : null;
-        $this->container['class'] = isset($data['class']) ? $data['class'] : null;
+        $this->container['name'] = $data['name'] ?? null;
+        $this->container['class'] = $data['class'] ?? null;
     }
 
     /**
@@ -226,7 +231,7 @@ public function getName()
      *
      * @param int|null $name name
      *
-     * @return $this
+     * @return self
      */
     public function setName($name)
     {
@@ -250,7 +255,7 @@ public function getClass()
      *
      * @param string|null $class class
      *
-     * @return $this
+     * @return self
      */
     public function setClass($class)
     {
@@ -275,18 +280,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelList.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelList.php
index 85335938efd3..dacecc851ab9 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelList.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelList.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class ModelList implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -64,6 +67,8 @@ class ModelList implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         '_123_list' => null
@@ -177,7 +182,7 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['_123_list'] = isset($data['_123_list']) ? $data['_123_list'] : null;
+        $this->container['_123_list'] = $data['_123_list'] ?? null;
     }
 
     /**
@@ -219,7 +224,7 @@ public function get123List()
      *
      * @param string|null $_123_list _123_list
      *
-     * @return $this
+     * @return self
      */
     public function set123List($_123_list)
     {
@@ -244,18 +249,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelReturn.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelReturn.php
index 7de6909e70b0..26f905224a05 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelReturn.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelReturn.php
@@ -40,10 +40,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class ModelReturn implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -65,6 +68,8 @@ class ModelReturn implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'return' => 'int32'
@@ -178,7 +183,7 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['return'] = isset($data['return']) ? $data['return'] : null;
+        $this->container['return'] = $data['return'] ?? null;
     }
 
     /**
@@ -220,7 +225,7 @@ public function getReturn()
      *
      * @param int|null $return return
      *
-     * @return $this
+     * @return self
      */
     public function setReturn($return)
     {
@@ -245,18 +250,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Name.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Name.php
index a3eddb499868..9f4fe7734c2c 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Name.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Name.php
@@ -40,10 +40,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class Name implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -68,6 +71,8 @@ class Name implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'name' => 'int32',
@@ -193,10 +198,10 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['name'] = isset($data['name']) ? $data['name'] : null;
-        $this->container['snake_case'] = isset($data['snake_case']) ? $data['snake_case'] : null;
-        $this->container['property'] = isset($data['property']) ? $data['property'] : null;
-        $this->container['_123_number'] = isset($data['_123_number']) ? $data['_123_number'] : null;
+        $this->container['name'] = $data['name'] ?? null;
+        $this->container['snake_case'] = $data['snake_case'] ?? null;
+        $this->container['property'] = $data['property'] ?? null;
+        $this->container['_123_number'] = $data['_123_number'] ?? null;
     }
 
     /**
@@ -241,7 +246,7 @@ public function getName()
      *
      * @param int $name name
      *
-     * @return $this
+     * @return self
      */
     public function setName($name)
     {
@@ -265,7 +270,7 @@ public function getSnakeCase()
      *
      * @param int|null $snake_case snake_case
      *
-     * @return $this
+     * @return self
      */
     public function setSnakeCase($snake_case)
     {
@@ -289,7 +294,7 @@ public function getProperty()
      *
      * @param string|null $property property
      *
-     * @return $this
+     * @return self
      */
     public function setProperty($property)
     {
@@ -313,7 +318,7 @@ public function get123Number()
      *
      * @param int|null $_123_number _123_number
      *
-     * @return $this
+     * @return self
      */
     public function set123Number($_123_number)
     {
@@ -338,18 +343,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/NullableClass.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/NullableClass.php
index 170f6a256fc9..f00792ef3649 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/NullableClass.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/NullableClass.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class NullableClass implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -75,6 +78,8 @@ class NullableClass implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'integer_prop' => null,
@@ -232,18 +237,18 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['integer_prop'] = isset($data['integer_prop']) ? $data['integer_prop'] : null;
-        $this->container['number_prop'] = isset($data['number_prop']) ? $data['number_prop'] : null;
-        $this->container['boolean_prop'] = isset($data['boolean_prop']) ? $data['boolean_prop'] : null;
-        $this->container['string_prop'] = isset($data['string_prop']) ? $data['string_prop'] : null;
-        $this->container['date_prop'] = isset($data['date_prop']) ? $data['date_prop'] : null;
-        $this->container['datetime_prop'] = isset($data['datetime_prop']) ? $data['datetime_prop'] : null;
-        $this->container['array_nullable_prop'] = isset($data['array_nullable_prop']) ? $data['array_nullable_prop'] : null;
-        $this->container['array_and_items_nullable_prop'] = isset($data['array_and_items_nullable_prop']) ? $data['array_and_items_nullable_prop'] : null;
-        $this->container['array_items_nullable'] = isset($data['array_items_nullable']) ? $data['array_items_nullable'] : null;
-        $this->container['object_nullable_prop'] = isset($data['object_nullable_prop']) ? $data['object_nullable_prop'] : null;
-        $this->container['object_and_items_nullable_prop'] = isset($data['object_and_items_nullable_prop']) ? $data['object_and_items_nullable_prop'] : null;
-        $this->container['object_items_nullable'] = isset($data['object_items_nullable']) ? $data['object_items_nullable'] : null;
+        $this->container['integer_prop'] = $data['integer_prop'] ?? null;
+        $this->container['number_prop'] = $data['number_prop'] ?? null;
+        $this->container['boolean_prop'] = $data['boolean_prop'] ?? null;
+        $this->container['string_prop'] = $data['string_prop'] ?? null;
+        $this->container['date_prop'] = $data['date_prop'] ?? null;
+        $this->container['datetime_prop'] = $data['datetime_prop'] ?? null;
+        $this->container['array_nullable_prop'] = $data['array_nullable_prop'] ?? null;
+        $this->container['array_and_items_nullable_prop'] = $data['array_and_items_nullable_prop'] ?? null;
+        $this->container['array_items_nullable'] = $data['array_items_nullable'] ?? null;
+        $this->container['object_nullable_prop'] = $data['object_nullable_prop'] ?? null;
+        $this->container['object_and_items_nullable_prop'] = $data['object_and_items_nullable_prop'] ?? null;
+        $this->container['object_items_nullable'] = $data['object_items_nullable'] ?? null;
     }
 
     /**
@@ -285,7 +290,7 @@ public function getIntegerProp()
      *
      * @param int|null $integer_prop integer_prop
      *
-     * @return $this
+     * @return self
      */
     public function setIntegerProp($integer_prop)
     {
@@ -309,7 +314,7 @@ public function getNumberProp()
      *
      * @param float|null $number_prop number_prop
      *
-     * @return $this
+     * @return self
      */
     public function setNumberProp($number_prop)
     {
@@ -333,7 +338,7 @@ public function getBooleanProp()
      *
      * @param bool|null $boolean_prop boolean_prop
      *
-     * @return $this
+     * @return self
      */
     public function setBooleanProp($boolean_prop)
     {
@@ -357,7 +362,7 @@ public function getStringProp()
      *
      * @param string|null $string_prop string_prop
      *
-     * @return $this
+     * @return self
      */
     public function setStringProp($string_prop)
     {
@@ -381,7 +386,7 @@ public function getDateProp()
      *
      * @param \DateTime|null $date_prop date_prop
      *
-     * @return $this
+     * @return self
      */
     public function setDateProp($date_prop)
     {
@@ -405,7 +410,7 @@ public function getDatetimeProp()
      *
      * @param \DateTime|null $datetime_prop datetime_prop
      *
-     * @return $this
+     * @return self
      */
     public function setDatetimeProp($datetime_prop)
     {
@@ -429,7 +434,7 @@ public function getArrayNullableProp()
      *
      * @param object[]|null $array_nullable_prop array_nullable_prop
      *
-     * @return $this
+     * @return self
      */
     public function setArrayNullableProp($array_nullable_prop)
     {
@@ -453,7 +458,7 @@ public function getArrayAndItemsNullableProp()
      *
      * @param object[]|null $array_and_items_nullable_prop array_and_items_nullable_prop
      *
-     * @return $this
+     * @return self
      */
     public function setArrayAndItemsNullableProp($array_and_items_nullable_prop)
     {
@@ -477,7 +482,7 @@ public function getArrayItemsNullable()
      *
      * @param object[]|null $array_items_nullable array_items_nullable
      *
-     * @return $this
+     * @return self
      */
     public function setArrayItemsNullable($array_items_nullable)
     {
@@ -501,7 +506,7 @@ public function getObjectNullableProp()
      *
      * @param map[string,object]|null $object_nullable_prop object_nullable_prop
      *
-     * @return $this
+     * @return self
      */
     public function setObjectNullableProp($object_nullable_prop)
     {
@@ -525,7 +530,7 @@ public function getObjectAndItemsNullableProp()
      *
      * @param map[string,object]|null $object_and_items_nullable_prop object_and_items_nullable_prop
      *
-     * @return $this
+     * @return self
      */
     public function setObjectAndItemsNullableProp($object_and_items_nullable_prop)
     {
@@ -549,7 +554,7 @@ public function getObjectItemsNullable()
      *
      * @param map[string,object]|null $object_items_nullable object_items_nullable
      *
-     * @return $this
+     * @return self
      */
     public function setObjectItemsNullable($object_items_nullable)
     {
@@ -574,18 +579,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/NumberOnly.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/NumberOnly.php
index 17b092299c13..0f4af94c9ff5 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/NumberOnly.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/NumberOnly.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class NumberOnly implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -64,6 +67,8 @@ class NumberOnly implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'just_number' => null
@@ -177,7 +182,7 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['just_number'] = isset($data['just_number']) ? $data['just_number'] : null;
+        $this->container['just_number'] = $data['just_number'] ?? null;
     }
 
     /**
@@ -219,7 +224,7 @@ public function getJustNumber()
      *
      * @param float|null $just_number just_number
      *
-     * @return $this
+     * @return self
      */
     public function setJustNumber($just_number)
     {
@@ -244,18 +249,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Order.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Order.php
index 0fce0df270cc..34084f1ea23a 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Order.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Order.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class Order implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -69,6 +72,8 @@ class Order implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'id' => 'int64',
@@ -219,12 +224,12 @@ public function getStatusAllowableValues()
      */
     public function __construct(array $data = null)
     {
-        $this->container['id'] = isset($data['id']) ? $data['id'] : null;
-        $this->container['pet_id'] = isset($data['pet_id']) ? $data['pet_id'] : null;
-        $this->container['quantity'] = isset($data['quantity']) ? $data['quantity'] : null;
-        $this->container['ship_date'] = isset($data['ship_date']) ? $data['ship_date'] : null;
-        $this->container['status'] = isset($data['status']) ? $data['status'] : null;
-        $this->container['complete'] = isset($data['complete']) ? $data['complete'] : false;
+        $this->container['id'] = $data['id'] ?? null;
+        $this->container['pet_id'] = $data['pet_id'] ?? null;
+        $this->container['quantity'] = $data['quantity'] ?? null;
+        $this->container['ship_date'] = $data['ship_date'] ?? null;
+        $this->container['status'] = $data['status'] ?? null;
+        $this->container['complete'] = $data['complete'] ?? false;
     }
 
     /**
@@ -274,7 +279,7 @@ public function getId()
      *
      * @param int|null $id id
      *
-     * @return $this
+     * @return self
      */
     public function setId($id)
     {
@@ -298,7 +303,7 @@ public function getPetId()
      *
      * @param int|null $pet_id pet_id
      *
-     * @return $this
+     * @return self
      */
     public function setPetId($pet_id)
     {
@@ -322,7 +327,7 @@ public function getQuantity()
      *
      * @param int|null $quantity quantity
      *
-     * @return $this
+     * @return self
      */
     public function setQuantity($quantity)
     {
@@ -346,7 +351,7 @@ public function getShipDate()
      *
      * @param \DateTime|null $ship_date ship_date
      *
-     * @return $this
+     * @return self
      */
     public function setShipDate($ship_date)
     {
@@ -370,7 +375,7 @@ public function getStatus()
      *
      * @param string|null $status Order Status
      *
-     * @return $this
+     * @return self
      */
     public function setStatus($status)
     {
@@ -403,7 +408,7 @@ public function getComplete()
      *
      * @param bool|null $complete complete
      *
-     * @return $this
+     * @return self
      */
     public function setComplete($complete)
     {
@@ -428,18 +433,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/OuterComposite.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/OuterComposite.php
index cab3e72a8c48..f2558176b29b 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/OuterComposite.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/OuterComposite.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class OuterComposite implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -66,6 +69,8 @@ class OuterComposite implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'my_number' => null,
@@ -187,9 +192,9 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['my_number'] = isset($data['my_number']) ? $data['my_number'] : null;
-        $this->container['my_string'] = isset($data['my_string']) ? $data['my_string'] : null;
-        $this->container['my_boolean'] = isset($data['my_boolean']) ? $data['my_boolean'] : null;
+        $this->container['my_number'] = $data['my_number'] ?? null;
+        $this->container['my_string'] = $data['my_string'] ?? null;
+        $this->container['my_boolean'] = $data['my_boolean'] ?? null;
     }
 
     /**
@@ -231,7 +236,7 @@ public function getMyNumber()
      *
      * @param float|null $my_number my_number
      *
-     * @return $this
+     * @return self
      */
     public function setMyNumber($my_number)
     {
@@ -255,7 +260,7 @@ public function getMyString()
      *
      * @param string|null $my_string my_string
      *
-     * @return $this
+     * @return self
      */
     public function setMyString($my_string)
     {
@@ -279,7 +284,7 @@ public function getMyBoolean()
      *
      * @param bool|null $my_boolean my_boolean
      *
-     * @return $this
+     * @return self
      */
     public function setMyBoolean($my_boolean)
     {
@@ -304,18 +309,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Pet.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Pet.php
index 4e341c3f60ec..7bbdafe09667 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Pet.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Pet.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class Pet implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -69,6 +72,8 @@ class Pet implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'id' => 'int64',
@@ -219,12 +224,12 @@ public function getStatusAllowableValues()
      */
     public function __construct(array $data = null)
     {
-        $this->container['id'] = isset($data['id']) ? $data['id'] : null;
-        $this->container['category'] = isset($data['category']) ? $data['category'] : null;
-        $this->container['name'] = isset($data['name']) ? $data['name'] : null;
-        $this->container['photo_urls'] = isset($data['photo_urls']) ? $data['photo_urls'] : null;
-        $this->container['tags'] = isset($data['tags']) ? $data['tags'] : null;
-        $this->container['status'] = isset($data['status']) ? $data['status'] : null;
+        $this->container['id'] = $data['id'] ?? null;
+        $this->container['category'] = $data['category'] ?? null;
+        $this->container['name'] = $data['name'] ?? null;
+        $this->container['photo_urls'] = $data['photo_urls'] ?? null;
+        $this->container['tags'] = $data['tags'] ?? null;
+        $this->container['status'] = $data['status'] ?? null;
     }
 
     /**
@@ -280,7 +285,7 @@ public function getId()
      *
      * @param int|null $id id
      *
-     * @return $this
+     * @return self
      */
     public function setId($id)
     {
@@ -304,7 +309,7 @@ public function getCategory()
      *
      * @param \OpenAPI\Client\Model\Category|null $category category
      *
-     * @return $this
+     * @return self
      */
     public function setCategory($category)
     {
@@ -328,7 +333,7 @@ public function getName()
      *
      * @param string $name name
      *
-     * @return $this
+     * @return self
      */
     public function setName($name)
     {
@@ -352,7 +357,7 @@ public function getPhotoUrls()
      *
      * @param string[] $photo_urls photo_urls
      *
-     * @return $this
+     * @return self
      */
     public function setPhotoUrls($photo_urls)
     {
@@ -376,7 +381,7 @@ public function getTags()
      *
      * @param \OpenAPI\Client\Model\Tag[]|null $tags tags
      *
-     * @return $this
+     * @return self
      */
     public function setTags($tags)
     {
@@ -400,7 +405,7 @@ public function getStatus()
      *
      * @param string|null $status pet status in the store
      *
-     * @return $this
+     * @return self
      */
     public function setStatus($status)
     {
@@ -434,18 +439,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ReadOnlyFirst.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ReadOnlyFirst.php
index 1cdb5ac74daf..d859ef1b6114 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ReadOnlyFirst.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ReadOnlyFirst.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class ReadOnlyFirst implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -65,6 +68,8 @@ class ReadOnlyFirst implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'bar' => null,
@@ -182,8 +187,8 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['bar'] = isset($data['bar']) ? $data['bar'] : null;
-        $this->container['baz'] = isset($data['baz']) ? $data['baz'] : null;
+        $this->container['bar'] = $data['bar'] ?? null;
+        $this->container['baz'] = $data['baz'] ?? null;
     }
 
     /**
@@ -225,7 +230,7 @@ public function getBar()
      *
      * @param string|null $bar bar
      *
-     * @return $this
+     * @return self
      */
     public function setBar($bar)
     {
@@ -249,7 +254,7 @@ public function getBaz()
      *
      * @param string|null $baz baz
      *
-     * @return $this
+     * @return self
      */
     public function setBaz($baz)
     {
@@ -274,18 +279,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/SpecialModelName.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/SpecialModelName.php
index b58e8fcff1e2..4ea1a0f26dee 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/SpecialModelName.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/SpecialModelName.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class SpecialModelName implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -64,6 +67,8 @@ class SpecialModelName implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'special_property_name' => 'int64'
@@ -177,7 +182,7 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['special_property_name'] = isset($data['special_property_name']) ? $data['special_property_name'] : null;
+        $this->container['special_property_name'] = $data['special_property_name'] ?? null;
     }
 
     /**
@@ -219,7 +224,7 @@ public function getSpecialPropertyName()
      *
      * @param int|null $special_property_name special_property_name
      *
-     * @return $this
+     * @return self
      */
     public function setSpecialPropertyName($special_property_name)
     {
@@ -244,18 +249,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Tag.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Tag.php
index 1c3dd48126d1..3eb455e0f7cc 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Tag.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Tag.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class Tag implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -65,6 +68,8 @@ class Tag implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'id' => 'int64',
@@ -182,8 +187,8 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['id'] = isset($data['id']) ? $data['id'] : null;
-        $this->container['name'] = isset($data['name']) ? $data['name'] : null;
+        $this->container['id'] = $data['id'] ?? null;
+        $this->container['name'] = $data['name'] ?? null;
     }
 
     /**
@@ -225,7 +230,7 @@ public function getId()
      *
      * @param int|null $id id
      *
-     * @return $this
+     * @return self
      */
     public function setId($id)
     {
@@ -249,7 +254,7 @@ public function getName()
      *
      * @param string|null $name name
      *
-     * @return $this
+     * @return self
      */
     public function setName($name)
     {
@@ -274,18 +279,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/User.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/User.php
index 859a20252490..4e40a57fd78a 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/User.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/User.php
@@ -39,10 +39,13 @@
  * @package  OpenAPI\Client
  * @author   OpenAPI Generator team
  * @link     https://openapi-generator.tech
+ * @implements \ArrayAccess<TKey, TValue>
+ * @template TKey int|null
+ * @template TValue mixed|null  
  */
 class User implements ModelInterface, ArrayAccess
 {
-    const DISCRIMINATOR = null;
+    public const DISCRIMINATOR = null;
 
     /**
       * The original name of the model.
@@ -71,6 +74,8 @@ class User implements ModelInterface, ArrayAccess
       * Array of property to format mappings. Used for (de)serialization
       *
       * @var string[]
+      * @phpstan-var array<string, string|null>
+      * @psalm-var array<string, string|null>
       */
     protected static $openAPIFormats = [
         'id' => 'int64',
@@ -212,14 +217,14 @@ public function getModelName()
      */
     public function __construct(array $data = null)
     {
-        $this->container['id'] = isset($data['id']) ? $data['id'] : null;
-        $this->container['username'] = isset($data['username']) ? $data['username'] : null;
-        $this->container['first_name'] = isset($data['first_name']) ? $data['first_name'] : null;
-        $this->container['last_name'] = isset($data['last_name']) ? $data['last_name'] : null;
-        $this->container['email'] = isset($data['email']) ? $data['email'] : null;
-        $this->container['password'] = isset($data['password']) ? $data['password'] : null;
-        $this->container['phone'] = isset($data['phone']) ? $data['phone'] : null;
-        $this->container['user_status'] = isset($data['user_status']) ? $data['user_status'] : null;
+        $this->container['id'] = $data['id'] ?? null;
+        $this->container['username'] = $data['username'] ?? null;
+        $this->container['first_name'] = $data['first_name'] ?? null;
+        $this->container['last_name'] = $data['last_name'] ?? null;
+        $this->container['email'] = $data['email'] ?? null;
+        $this->container['password'] = $data['password'] ?? null;
+        $this->container['phone'] = $data['phone'] ?? null;
+        $this->container['user_status'] = $data['user_status'] ?? null;
     }
 
     /**
@@ -261,7 +266,7 @@ public function getId()
      *
      * @param int|null $id id
      *
-     * @return $this
+     * @return self
      */
     public function setId($id)
     {
@@ -285,7 +290,7 @@ public function getUsername()
      *
      * @param string|null $username username
      *
-     * @return $this
+     * @return self
      */
     public function setUsername($username)
     {
@@ -309,7 +314,7 @@ public function getFirstName()
      *
      * @param string|null $first_name first_name
      *
-     * @return $this
+     * @return self
      */
     public function setFirstName($first_name)
     {
@@ -333,7 +338,7 @@ public function getLastName()
      *
      * @param string|null $last_name last_name
      *
-     * @return $this
+     * @return self
      */
     public function setLastName($last_name)
     {
@@ -357,7 +362,7 @@ public function getEmail()
      *
      * @param string|null $email email
      *
-     * @return $this
+     * @return self
      */
     public function setEmail($email)
     {
@@ -381,7 +386,7 @@ public function getPassword()
      *
      * @param string|null $password password
      *
-     * @return $this
+     * @return self
      */
     public function setPassword($password)
     {
@@ -405,7 +410,7 @@ public function getPhone()
      *
      * @param string|null $phone phone
      *
-     * @return $this
+     * @return self
      */
     public function setPhone($phone)
     {
@@ -429,7 +434,7 @@ public function getUserStatus()
      *
      * @param int|null $user_status User Status
      *
-     * @return $this
+     * @return self
      */
     public function setUserStatus($user_status)
     {
@@ -454,18 +459,18 @@ public function offsetExists($offset)
      *
      * @param integer $offset Offset
      *
-     * @return mixed
+     * @return mixed|null
      */
     public function offsetGet($offset)
     {
-        return isset($this->container[$offset]) ? $this->container[$offset] : null;
+        return isset($this->container[$offset]) ?? null;
     }
 
     /**
      * Sets value based on offset.
      *
-     * @param integer $offset Offset
-     * @param mixed   $value  Value to be set
+     * @param int|null $offset Offset
+     * @param mixed    $value  Value to be set
      *
      * @return void
      */
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php b/samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php
index 4c7108c94b6f..8ca97b47c842 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php
@@ -61,20 +61,26 @@ public static function setDateTimeFormat($format)
      * @param string $type   the OpenAPIToolsType of the data
      * @param string $format the format of the OpenAPITools type of the data
      *
-     * @return string|object serialized form of $data
+     * @return scalar|object|array|null serialized form of $data
      */
     public static function sanitizeForSerialization($data, $type = null, $format = null)
     {
         if (is_scalar($data) || null === $data) {
             return $data;
-        } elseif ($data instanceof \DateTime) {
+        }
+
+        if ($data instanceof \DateTime) {
             return ($format === 'date') ? $data->format('Y-m-d') : $data->format(self::$dateTimeFormat);
-        } elseif (is_array($data)) {
+        }
+
+        if (is_array($data)) {
             foreach ($data as $property => $value) {
                 $data[$property] = self::sanitizeForSerialization($value);
             }
             return $data;
-        } elseif (is_object($data)) {
+        }
+
+        if (is_object($data)) {
             $values = [];
             if ($data instanceof ModelInterface) {
                 $formats = $data::openAPIFormats();
@@ -260,7 +266,9 @@ public static function deserialize($data, $class, $httpHeaders = null)
     {
         if (null === $data) {
             return null;
-        } elseif (strcasecmp(substr($class, -2), '[]') === 0) {
+        }
+
+        if (strcasecmp(substr($class, -2), '[]') === 0) {
             $data = is_string($data) ? json_decode($data) : $data;
             
             if (!is_array($data)) {
@@ -273,7 +281,9 @@ public static function deserialize($data, $class, $httpHeaders = null)
                 $values[] = self::deserialize($value, $subClass, null);
             }
             return $values;
-        } elseif (substr($class, 0, 4) === 'map[') { // for associative array e.g. map[string,int]
+        }
+
+        if (substr($class, 0, 4) === 'map[') { // for associative array e.g. map[string,int]
             $data = is_string($data) ? json_decode($data) : $data;
             settype($data, 'array');
             $inner = substr($class, 4, -1);
@@ -286,10 +296,14 @@ public static function deserialize($data, $class, $httpHeaders = null)
                 }
             }
             return $deserialized;
-        } elseif ($class === 'object') {
+        }
+
+        if ($class === 'object') {
             settype($data, 'array');
             return $data;
-        } elseif ($class === '\DateTime') {
+        }
+
+        if ($class === '\DateTime') {
             // Some API's return an invalid, empty string as a
             // date-time property. DateTime::__construct() will return
             // the current time for empty input which is probably not
@@ -301,10 +315,14 @@ public static function deserialize($data, $class, $httpHeaders = null)
             } else {
                 return null;
             }
-        } elseif (in_array($class, ['DateTime', 'bool', 'boolean', 'byte', 'double', 'float', 'int', 'integer', 'mixed', 'number', 'object', 'string', 'void'], true)) {
+        }
+
+        if (in_array($class, ['DateTime', 'bool', 'boolean', 'byte', 'double', 'float', 'int', 'integer', 'mixed', 'number', 'object', 'string', 'void'], true)) {
             settype($data, $class);
             return $data;
-        } elseif ($class === '\SplFileObject') {
+        }
+
+        if ($class === '\SplFileObject') {
             /** @var \Psr\Http\Message\StreamInterface $data */
 
             // determine file name