diff --git a/docs/en/02_Developer_Guides/19_GraphQL/05_plugins/03_writing_a_complex_plugin.md b/docs/en/02_Developer_Guides/19_GraphQL/05_plugins/03_writing_a_complex_plugin.md
index 8d5344a8fee..6748399009e 100644
--- a/docs/en/02_Developer_Guides/19_GraphQL/05_plugins/03_writing_a_complex_plugin.md
+++ b/docs/en/02_Developer_Guides/19_GraphQL/05_plugins/03_writing_a_complex_plugin.md
@@ -56,7 +56,7 @@ class GeocodableDataObject implements ModelTypePlugin
         );
 
         // only apply the plugin to geocodable DataObjects
-        if (!Extensible::has_extension($class, Geocodable::class)) {
+        if (!ViewableData::has_extension($class, Geocodable::class)) {
             return;
         }
 
@@ -85,7 +85,7 @@ class GeocodableQuery implements ModelQueryPlugin
     {
         $class = $query->getModel()->getSourceClass();
         // Only apply to geocodable objects
-        if (!Extensible::has_extension($class, Geocodable::class)) {
+        if (!ViewableData::has_extension($class, Geocodable::class)) {
             return;
         }
 
@@ -177,7 +177,7 @@ public function apply(ModelQuery $query, Schema $schema, array $config = []): vo
 {
     $class = $query->getModel()->getSourceClass();
     // Only apply to geocodable objects
-    if (!Extensible::has_extension($class, Geocodable::class)) {
+    if (!ViewableData::has_extension($class, Geocodable::class)) {
         return;
     }
 
diff --git a/src/Control/HTTP.php b/src/Control/HTTP.php
index 61c9bdabd60..f15d4f877ae 100644
--- a/src/Control/HTTP.php
+++ b/src/Control/HTTP.php
@@ -259,7 +259,7 @@ public static function setGetVar($varname, $varvalue, $currentURL = null, $separ
         $path = (isset($parts['path']) && $parts['path'] != '') ? $parts['path'] : '';
 
         // handle URL params which are existing / new
-        $params = ($params) ? '?' . http_build_query($params, null, $separator) : '';
+        $params = ($params) ? '?' . http_build_query($params, '', $separator) : '';
 
         // keep fragments (anchors) intact.
         $fragment = (isset($parts['fragment']) && $parts['fragment'] != '') ? '#' . $parts['fragment'] : '';
diff --git a/src/Control/HTTPResponse_Exception.php b/src/Control/HTTPResponse_Exception.php
index 5075765179f..355e28000f4 100644
--- a/src/Control/HTTPResponse_Exception.php
+++ b/src/Control/HTTPResponse_Exception.php
@@ -49,7 +49,7 @@ public function __construct($body = null, $statusCode = null, $statusDescription
             $this->setResponse($response);
         }
 
-        parent::__construct($this->getResponse()->getBody(), $this->getResponse()->getStatusCode());
+        parent::__construct((string) $this->getResponse()->getBody(), $this->getResponse()->getStatusCode());
     }
 
     /**
diff --git a/src/Core/ClassInfo.php b/src/Core/ClassInfo.php
index 0c98e9cd863..736dd7e5530 100644
--- a/src/Core/ClassInfo.php
+++ b/src/Core/ClassInfo.php
@@ -10,6 +10,7 @@
 use SilverStripe\Dev\Deprecation;
 use SilverStripe\ORM\DataObject;
 use SilverStripe\ORM\DB;
+use SilverStripe\View\ViewableData;
 
 /**
  * Provides introspection information about the class tree.
@@ -597,7 +598,7 @@ public static function classesWithExtension(
 
         // only keep classes with the Extension applied
         $classes = array_filter($classes, function ($class) use ($extensionClass) {
-            return Extensible::has_extension($class, $extensionClass);
+            return ViewableData::has_extension($class, $extensionClass);
         });
 
         return $classes;
diff --git a/src/Dev/CSVParser.php b/src/Dev/CSVParser.php
index 1b23a866194..3d99426c300 100644
--- a/src/Dev/CSVParser.php
+++ b/src/Dev/CSVParser.php
@@ -168,7 +168,6 @@ public function provideHeaderRow($headerRow)
      */
     protected function openFile()
     {
-        ini_set('auto_detect_line_endings', 1);
         $this->fileHandle = fopen($this->filename, 'r');
 
         if ($this->providedHeaderRow) {
diff --git a/src/Dev/CsvBulkLoader.php b/src/Dev/CsvBulkLoader.php
index 07b12b867e4..94708eabab5 100644
--- a/src/Dev/CsvBulkLoader.php
+++ b/src/Dev/CsvBulkLoader.php
@@ -68,9 +68,6 @@ public function preview($filepath)
      */
     protected function processAll($filepath, $preview = false)
     {
-        $previousDetectLE = ini_get('auto_detect_line_endings');
-        ini_set('auto_detect_line_endings', true);
-
         $this->extend('onBeforeProcessAll', $filepath, $preview);
 
         $result = BulkLoader_Result::create();
@@ -144,8 +141,6 @@ protected function processAll($filepath, $preview = false)
                 $failedMessage = sprintf($failedMessage . " because %s", $e->getMessage());
             }
             print $failedMessage . PHP_EOL;
-        } finally {
-            ini_set('auto_detect_line_endings', $previousDetectLE);
         }
 
         $this->extend('onAfterProcessAll', $result, $preview);
@@ -182,9 +177,6 @@ protected function getNormalisedColumnMap()
     protected function splitFile($path, $lines = null)
     {
         Deprecation::notice('5.0', 'splitFile is deprecated, please process files using a stream');
-        $previous = ini_get('auto_detect_line_endings');
-
-        ini_set('auto_detect_line_endings', true);
 
         if (!is_int($lines)) {
             $lines = $this->config()->get("lines");
@@ -230,11 +222,8 @@ protected function splitFile($path, $lines = null)
                 $count = 0;
             }
         }
-
         fclose($to);
 
-        ini_set('auto_detect_line_endings', $previous);
-
         return $files;
     }
 
diff --git a/src/ORM/FieldType/DBDecimal.php b/src/ORM/FieldType/DBDecimal.php
index 92394770d33..0ecf6c6bd0c 100644
--- a/src/ORM/FieldType/DBDecimal.php
+++ b/src/ORM/FieldType/DBDecimal.php
@@ -126,7 +126,7 @@ public function prepValueForDB($value)
             return 0;
         }
 
-        if (ctype_digit($value)) {
+        if (ctype_digit((string) $value)) {
             return (int)$value;
         }
 
diff --git a/src/ORM/Hierarchy/Hierarchy.php b/src/ORM/Hierarchy/Hierarchy.php
index 6f6d2e84c2c..6293273bc65 100644
--- a/src/ORM/Hierarchy/Hierarchy.php
+++ b/src/ORM/Hierarchy/Hierarchy.php
@@ -5,7 +5,6 @@
 use SilverStripe\Admin\LeftAndMain;
 use SilverStripe\Control\Controller;
 use SilverStripe\Core\ClassInfo;
-use SilverStripe\Core\Extensible;
 use SilverStripe\ORM\DataList;
 use SilverStripe\ORM\SS_List;
 use SilverStripe\ORM\ValidationResult;
@@ -17,6 +16,7 @@
 use SilverStripe\Core\Config\Config;
 use SilverStripe\Core\Convert;
 use Exception;
+use SilverStripe\View\ViewableData;
 
 /**
  * DataObjects that use the Hierarchy extension can be be organised as a hierarchy, with children and parents. The most
@@ -418,7 +418,7 @@ private function getHierarchyBaseClass(): string
     {
         $ancestry = ClassInfo::ancestry($this->owner);
         $ancestorClass = array_shift($ancestry);
-        while ($ancestorClass && !Extensible::has_extension($ancestorClass, self::class)) {
+        while ($ancestorClass && !ViewableData::has_extension($ancestorClass, self::class)) {
             $ancestorClass = array_shift($ancestry);
         }
 
diff --git a/src/View/Parsers/HTMLValue.php b/src/View/Parsers/HTMLValue.php
index 8809bad5da5..a5ee8b7134c 100644
--- a/src/View/Parsers/HTMLValue.php
+++ b/src/View/Parsers/HTMLValue.php
@@ -146,7 +146,7 @@ public function __call($method, $arguments)
     {
         $doc = $this->getDocument();
 
-        if (method_exists($doc, $method)) {
+        if ($doc && method_exists($doc, $method)) {
             return call_user_func_array([$doc, $method], $arguments);
         } else {
             return parent::__call($method, $arguments);
diff --git a/tests/php/Forms/DatetimeFieldTest.php b/tests/php/Forms/DatetimeFieldTest.php
index cf77ab75f22..af1090784c4 100644
--- a/tests/php/Forms/DatetimeFieldTest.php
+++ b/tests/php/Forms/DatetimeFieldTest.php
@@ -2,6 +2,7 @@
 
 namespace SilverStripe\Forms\Tests;
 
+use IntlDateFormatter;
 use SilverStripe\Control\Controller;
 use SilverStripe\Dev\SapphireTest;
 use SilverStripe\Forms\DatetimeField;
@@ -256,12 +257,12 @@ public function testValidateMinDateStrtotime()
     {
         $f = new DatetimeField('Datetime');
         $f->setMinDatetime('-7 days');
-        $f->setValue(strftime('%Y-%m-%d %T', strtotime('-8 days', DBDatetime::now()->getTimestamp())));
+        $f->setValue(date('Y-m-d H:i:s', strtotime('-8 days', DBDatetime::now()->getTimestamp())));
         $this->assertFalse($f->validate(new RequiredFields()), 'Date below min datetime, with strtotime');
 
         $f = new DatetimeField('Datetime');
         $f->setMinDatetime('-7 days');
-        $f->setValue(strftime('%Y-%m-%d %T', strtotime('-7 days', DBDatetime::now()->getTimestamp())));
+        $f->setValue(date('Y-m-d H:i:s', strtotime('-7 days', DBDatetime::now()->getTimestamp())));
         $this->assertTrue($f->validate(new RequiredFields()), 'Date matching min datetime, with strtotime');
     }
 
@@ -269,12 +270,12 @@ public function testValidateMaxDateStrtotime()
     {
         $f = new DatetimeField('Datetime');
         $f->setMaxDatetime('7 days');
-        $f->setValue(strftime('%Y-%m-%d %T', strtotime('8 days', DBDatetime::now()->getTimestamp())));
+        $f->setValue(date('Y-m-d H:i:s', strtotime('8 days', DBDatetime::now()->getTimestamp())));
         $this->assertFalse($f->validate(new RequiredFields()), 'Date above max date, with strtotime');
 
         $f = new DatetimeField('Datetime');
         $f->setMaxDatetime('7 days');
-        $f->setValue(strftime('%Y-%m-%d %T', strtotime('7 days', DBDatetime::now()->getTimestamp())));
+        $f->setValue(date('Y-m-d H:i:s', strtotime('7 days', DBDatetime::now()->getTimestamp())));
         $this->assertTrue($f->validate(new RequiredFields()), 'Date matching max date, with strtotime');
     }
 
diff --git a/tests/php/Forms/FormTest.php b/tests/php/Forms/FormTest.php
index e0d2a9a2676..0ccb35f8f1d 100644
--- a/tests/php/Forms/FormTest.php
+++ b/tests/php/Forms/FormTest.php
@@ -1143,8 +1143,8 @@ protected function clean($input)
     {
         return str_replace(
             [
-                html_entity_decode(' ', null, 'UTF-8'),
-                html_entity_decode(' ', null, 'UTF-8'), // narrow non-breaking space
+                html_entity_decode(' ', 0, 'UTF-8'),
+                html_entity_decode(' ', 0, 'UTF-8'), // narrow non-breaking space
             ],
             ' ',
             trim($input)
diff --git a/tests/php/Forms/NumericFieldTest.php b/tests/php/Forms/NumericFieldTest.php
index f7aa46b4d00..8bf3e9ef6c9 100644
--- a/tests/php/Forms/NumericFieldTest.php
+++ b/tests/php/Forms/NumericFieldTest.php
@@ -24,8 +24,8 @@ protected function clean($input)
     {
         return str_replace(
             [
-                html_entity_decode(' ', null, 'UTF-8'),
-                html_entity_decode(' ', null, 'UTF-8'), // narrow non-breaking space
+                html_entity_decode(' ', 0, 'UTF-8'),
+                html_entity_decode(' ', 0, 'UTF-8'), // narrow non-breaking space
             ],
             ' ',
             trim($input)
diff --git a/tests/php/ORM/DBMoneyTest.php b/tests/php/ORM/DBMoneyTest.php
index a231f6aac51..9709614b513 100644
--- a/tests/php/ORM/DBMoneyTest.php
+++ b/tests/php/ORM/DBMoneyTest.php
@@ -350,7 +350,7 @@ public function testHasAmount()
      */
     protected function clean($input)
     {
-        $nbsp = html_entity_decode(' ', null, 'UTF-8');
+        $nbsp = html_entity_decode(' ', 0, 'UTF-8');
         return str_replace(' ', $nbsp, trim($input));
     }
 }