diff --git a/system/src/Grav/Framework/Collection/AbstractIndexCollection.php b/system/src/Grav/Framework/Collection/AbstractIndexCollection.php
index 341c2e078..9d7d6bb3d 100644
--- a/system/src/Grav/Framework/Collection/AbstractIndexCollection.php
+++ b/system/src/Grav/Framework/Collection/AbstractIndexCollection.php
@@ -407,7 +407,7 @@ abstract class AbstractIndexCollection implements CollectionInterface
         $keys = $this->getKeys();
         shuffle($keys);
 
-        return $this->createFrom(array_replace(array_flip($keys), $this->entries) ?? []);
+        return $this->createFrom(array_replace(array_flip($keys), $this->entries));
     }
 
     /**
diff --git a/system/src/Grav/Framework/Flex/Flex.php b/system/src/Grav/Framework/Flex/Flex.php
index e60dc50e1..28dc94345 100644
--- a/system/src/Grav/Framework/Flex/Flex.php
+++ b/system/src/Grav/Framework/Flex/Flex.php
@@ -62,7 +62,7 @@ class Flex implements FlexInterface
      */
     public function addDirectoryType(string $type, string $blueprint, array $config = [])
     {
-        $config = array_replace_recursive(['enabled' => true], $this->config ?? [], $config);
+        $config = array_replace_recursive(['enabled' => true], $this->config, $config);
 
         $this->types[$type] = new FlexDirectory($type, $blueprint, $config);
 
@@ -143,7 +143,7 @@ class Flex implements FlexInterface
     public function getMixedCollection(array $keys, array $options = []): FlexCollectionInterface
     {
         $collectionClass = $options['collection_class'] ?? ObjectCollection::class;
-        if (!class_exists($collectionClass)) {
+        if (!is_a($collectionClass, FlexCollectionInterface::class, true)) {
             throw new RuntimeException(sprintf('Cannot create collection: Class %s does not exist', $collectionClass));
         }
 
@@ -233,7 +233,7 @@ class Flex implements FlexInterface
 
         // Use the original key ordering.
         if (!$guessed) {
-            $list = array_replace(array_fill_keys($keys, null), $list) ?? [];
+            $list = array_replace(array_fill_keys($keys, null), $list);
         } else {
             // We have mixed keys, we need to map flex keys back to storage keys.
             $results = [];
diff --git a/system/src/Grav/Framework/Flex/FlexCollection.php b/system/src/Grav/Framework/Flex/FlexCollection.php
index 48d18ef0f..2a8a16712 100644
--- a/system/src/Grav/Framework/Flex/FlexCollection.php
+++ b/system/src/Grav/Framework/Flex/FlexCollection.php
@@ -47,7 +47,7 @@ class FlexCollection extends ObjectCollection implements FlexCollectionInterface
     private $_flexDirectory;
 
     /** @var string */
-    private $_keyField;
+    private $_keyField = 'storage_key';
 
     /**
      * Get list of cached methods.
@@ -487,7 +487,7 @@ class FlexCollection extends ObjectCollection implements FlexCollectionInterface
      */
     public function getKeyField(): string
     {
-        return $this->_keyField ?? 'storage_key';
+        return $this->_keyField;
     }
 
     /**
diff --git a/system/src/Grav/Framework/Flex/FlexDirectory.php b/system/src/Grav/Framework/Flex/FlexDirectory.php
index c84e3d185..a96ff6bed 100644
--- a/system/src/Grav/Framework/Flex/FlexDirectory.php
+++ b/system/src/Grav/Framework/Flex/FlexDirectory.php
@@ -495,6 +495,9 @@ class FlexDirectory implements FlexDirectoryInterface
     {
         /** @phpstan-var class-string $className */
         $className = $this->objectClassName ?: $this->getObjectClass();
+        if (!is_a($className, FlexObjectInterface::class, true)) {
+            throw new \RuntimeException('Bad object class: ' . $className);
+        }
 
         return new $className($data, $key, $this, $validate);
     }
@@ -509,6 +512,9 @@ class FlexDirectory implements FlexDirectoryInterface
     {
         /** phpstan-var class-string $className */
         $className = $this->collectionClassName ?: $this->getCollectionClass();
+        if (!is_a($className, FlexCollectionInterface::class, true)) {
+            throw new \RuntimeException('Bad collection class: ' . $className);
+        }
 
         return $className::createFromArray($entries, $this, $keyField);
     }
@@ -523,6 +529,9 @@ class FlexDirectory implements FlexDirectoryInterface
     {
         /** @phpstan-var class-string $className */
         $className = $this->indexClassName ?: $this->getIndexClass();
+        if (!is_a($className, FlexIndexInterface::class, true)) {
+            throw new \RuntimeException('Bad index class: ' . $className);
+        }
 
         return $className::createFromArray($entries, $this, $keyField);
     }
diff --git a/system/src/Grav/Framework/Flex/FlexIndex.php b/system/src/Grav/Framework/Flex/FlexIndex.php
index 98b26679f..14a48f5a4 100644
--- a/system/src/Grav/Framework/Flex/FlexIndex.php
+++ b/system/src/Grav/Framework/Flex/FlexIndex.php
@@ -40,14 +40,14 @@ use function in_array;
  * @implements FlexIndexInterface<T>
  * @mixin C
  */
-class FlexIndex extends ObjectIndex implements FlexCollectionInterface, FlexIndexInterface
+class FlexIndex extends ObjectIndex implements FlexIndexInterface
 {
     const VERSION = 1;
 
     /** @var FlexDirectory|null */
     private $_flexDirectory;
     /** @var string */
-    private $_keyField;
+    private $_keyField = 'storage_key';
     /** @var array */
     private $_indexKeys;
 
@@ -353,7 +353,7 @@ class FlexIndex extends ObjectIndex implements FlexCollectionInterface, FlexInde
      */
     public function getKeyField(): string
     {
-        return $this->_keyField ?? 'storage_key';
+        return $this->_keyField;
     }
 
     /**
@@ -416,7 +416,7 @@ class FlexIndex extends ObjectIndex implements FlexCollectionInterface, FlexInde
             $previous = $search;
         }
 
-        return $this->createFrom(array_replace($previous ?? [], $this->getEntries()) ?? []);
+        return $this->createFrom(array_replace($previous ?? [], $this->getEntries()));
     }
 
     /**
diff --git a/system/src/Grav/Framework/Flex/FlexObject.php b/system/src/Grav/Framework/Flex/FlexObject.php
index f77059225..f4987a43c 100644
--- a/system/src/Grav/Framework/Flex/FlexObject.php
+++ b/system/src/Grav/Framework/Flex/FlexObject.php
@@ -888,8 +888,8 @@ class FlexObject implements FlexObjectInterface, FlexAuthorizeInterface
     public function getDefaultValue(string $name, string $separator = null)
     {
         $separator = $separator ?: '.';
-        $path = explode($separator, $name) ?: [];
-        $offset = array_shift($path) ?? '';
+        $path = explode($separator, $name);
+        $offset = array_shift($path);
 
         $current = $this->getDefaultValues();
 
diff --git a/system/src/Grav/Framework/Flex/Pages/Traits/PageContentTrait.php b/system/src/Grav/Framework/Flex/Pages/Traits/PageContentTrait.php
index f534c132c..0fac6d608 100644
--- a/system/src/Grav/Framework/Flex/Pages/Traits/PageContentTrait.php
+++ b/system/src/Grav/Framework/Flex/Pages/Traits/PageContentTrait.php
@@ -288,7 +288,7 @@ trait PageContentTrait
             'process',
             $var,
             function ($value) {
-                $value = array_replace(Grav::instance()['config']->get('system.pages.process', []), is_array($value) ? $value : []) ?? [];
+                $value = array_replace(Grav::instance()['config']->get('system.pages.process', []), is_array($value) ? $value : []);
                 foreach ($value as $process => $status) {
                     $value[$process] = (bool)$status;
                 }
@@ -664,6 +664,7 @@ trait PageContentTrait
      */
     protected function processContent($content): string
     {
+        $content = is_string($content) ? $content : '';
         $grav = Grav::instance();
 
         /** @var Config $config */
@@ -676,7 +677,6 @@ trait PageContentTrait
         $twig_first = $this->getNestedProperty('header.twig_first') ?? $config->get('system.pages.twig_first', false);
         $never_cache_twig = $this->getNestedProperty('header.never_cache_twig') ?? $config->get('system.pages.never_cache_twig', false);
 
-        $cached = null;
         if ($cache_enable) {
             $cache = $this->getCache('render');
             $key = md5($this->getCacheKey() . '-content');
@@ -688,12 +688,10 @@ trait PageContentTrait
                 if ($process_twig && $never_cache_twig) {
                     $this->_content = $this->processTwig($this->_content);
                 }
-            } else {
-                $cached = null;
             }
         }
 
-        if (!$cached) {
+        if (null === $this->_content) {
             $markdown_options = [];
             if ($process_markdown) {
                 // Build markdown options.
diff --git a/system/src/Grav/Framework/Flex/Storage/AbstractFilesystemStorage.php b/system/src/Grav/Framework/Flex/Storage/AbstractFilesystemStorage.php
index 1934f50cf..2e3132146 100644
--- a/system/src/Grav/Framework/Flex/Storage/AbstractFilesystemStorage.php
+++ b/system/src/Grav/Framework/Flex/Storage/AbstractFilesystemStorage.php
@@ -127,6 +127,10 @@ abstract class AbstractFilesystemStorage implements FlexStorageInterface
         $formatterClassName = $formatter['class'] ?? JsonFormatter::class;
         $formatterOptions = $formatter['options'] ?? [];
 
+        if (!is_a($formatterClassName, FileFormatterInterface::class, true)) {
+            throw new \InvalidArgumentException('Bad Data Formatter');
+        }
+
         $this->dataFormatter = new $formatterClassName($formatterOptions);
     }
 
diff --git a/system/src/Grav/Framework/Flex/Traits/FlexMediaTrait.php b/system/src/Grav/Framework/Flex/Traits/FlexMediaTrait.php
index 66c868852..c2bc66891 100644
--- a/system/src/Grav/Framework/Flex/Traits/FlexMediaTrait.php
+++ b/system/src/Grav/Framework/Flex/Traits/FlexMediaTrait.php
@@ -44,7 +44,7 @@ trait FlexMediaTrait
     }
 
     /** @var array */
-    protected $_uploads;
+    protected $_uploads = [];
 
     /**
      * @return string|null
@@ -119,7 +119,7 @@ trait FlexMediaTrait
 
         // Load settings for the field.
         $schema = $this->getBlueprint()->schema();
-        $settings = $field && is_object($schema) ? (array)$schema->getProperty($field) : null;
+        $settings = (array)$schema->getProperty($field);
         if (!is_array($settings)) {
             return null;
         }
@@ -405,7 +405,7 @@ trait FlexMediaTrait
      */
     protected function getUpdatedMedia(): array
     {
-        return $this->_uploads ?? [];
+        return $this->_uploads;
     }
 
     /**