diff --git a/src/Forms/ResultConditionsField.php b/src/Forms/ResultConditionsField.php
index 15a9d95..c59ec21 100644
--- a/src/Forms/ResultConditionsField.php
+++ b/src/Forms/ResultConditionsField.php
@@ -43,7 +43,7 @@ public function Type()
     public function performReadonlyTransformation()
     {
         // If we have no value then defer to the parent that renders a "none" field
-        $value = trim($this->Value());
+        $value = trim((string) $this->Value());
         if (empty($value)) {
             return parent::performReadonlyTransformation();
         }
diff --git a/src/Model/ResourceFilter/Dropdown.php b/src/Model/ResourceFilter/Dropdown.php
index b21100e..2faef39 100644
--- a/src/Model/ResourceFilter/Dropdown.php
+++ b/src/Model/ResourceFilter/Dropdown.php
@@ -56,7 +56,7 @@ public function getClientConfig()
      */
     protected function getConfiguredOptions()
     {
-        $spec = json_decode($this->Options, true) ?: [];
+        $spec = json_decode((string) $this->Options, true) ?: [];
 
         if (!isset($spec['selectType'])) {
             return [];
diff --git a/src/Page/CKANRegistryPageController.php b/src/Page/CKANRegistryPageController.php
index 10c38e4..e608215 100644
--- a/src/Page/CKANRegistryPageController.php
+++ b/src/Page/CKANRegistryPageController.php
@@ -121,6 +121,6 @@ public function getBasePath(DataObject $holder = null)
         }
 
         $link = $holder->RelativeLink();
-        return Director::baseURL() . trim($link, '/');
+        return Director::baseURL() . trim((string) $link, '/');
     }
 }
diff --git a/src/Service/APIClient.php b/src/Service/APIClient.php
index f747322..da99b2c 100644
--- a/src/Service/APIClient.php
+++ b/src/Service/APIClient.php
@@ -44,7 +44,7 @@ public function getData(Resource $resource, $action = 'datastore_search', $id =
     {
         $endpoint = sprintf(
             '%s/api/%s/action/%s?id=%s',
-            trim($resource->Endpoint, '/'),
+            trim((string) $resource->Endpoint, '/'),
             APIClientInterface::API_VERSION,
             $action,
             $resource->{$id}
@@ -63,11 +63,11 @@ public function getData(Resource $resource, $action = 'datastore_search', $id =
             throw new RuntimeException('CKAN API is not available. Error code ' . $statusCode);
         }
 
-        if (!count(preg_grep('#application/json#', $response->getHeader('Content-Type')))) {
+        if (!count(preg_grep('#application/json#', $response->getHeader('Content-Type') ?: []) ?: [])) {
             throw new RuntimeException('CKAN API returns an invalid response: Content-Type is not JSON');
         }
 
-        $responseBody = json_decode($response->getBody()->getContents(), true);
+        $responseBody = json_decode((string) $response->getBody()->getContents(), true);
 
         if (!$responseBody || !isset($responseBody['success']) || !$responseBody['success']) {
             throw new RuntimeException('CKAN API returns an invalid response: Responded as invalid');
diff --git a/src/Service/ResourcePopulator.php b/src/Service/ResourcePopulator.php
index 19cb5fe..4556a52 100644
--- a/src/Service/ResourcePopulator.php
+++ b/src/Service/ResourcePopulator.php
@@ -116,18 +116,18 @@ protected function validateResource(Resource $resource)
     protected function parseName($id)
     {
         // Parse "camelCase" to "space case"
-        $name = strtolower(preg_replace('/(?<=[a-z\d])([A-Z])/', ' \1', $id));
+        $name = strtolower((string) preg_replace('/(?<=[a-z\d])([A-Z])/', ' \1', $id ?: ''));
 
         // Swap out certain characters with spaces
-        $name = str_replace(['_', '-'], ' ', $name);
+        $name = str_replace(['_', '-'], ' ', $name ?: '');
 
         // Remove some non-alphanumeric characters
-        $name = trim(preg_replace('/[^\/\w\s]/', '', $name));
+        $name = trim((string) preg_replace('/[^\/\w\s]/', '', $name ?: ''));
 
         // Remove extra spaces around slashes
-        $name = str_replace(' / ', '/', $name);
+        $name = str_replace(' / ', '/', $name ?: '');
 
-        return ucfirst($name);
+        return ucfirst((string) $name);
     }
 
     /**
diff --git a/tests/php/Forms/GridField/GridFieldDetailForm/ResourceFieldItemRequestTest.php b/tests/php/Forms/GridField/GridFieldDetailForm/ResourceFieldItemRequestTest.php
index 55f8ec4..923154b 100644
--- a/tests/php/Forms/GridField/GridFieldDetailForm/ResourceFieldItemRequestTest.php
+++ b/tests/php/Forms/GridField/GridFieldDetailForm/ResourceFieldItemRequestTest.php
@@ -143,7 +143,7 @@ protected function assertArrayEqualsInOrder($expected, $actual)
             '. Actual: ' . print_r($actual, true);
 
         foreach ($actual as $key => $value) {
-            $expectedKey = key($expected);
+            $expectedKey = key($expected ?: []);
             $expectedValue = array_shift($expected);
             $this->assertSame($expectedKey, $key, $message);
             $this->assertEquals($expectedValue, $value, $message);