diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 97d9b749f..063e23647 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -20,6 +20,7 @@ jobs:
           - '8.1'
           - '8.2'
           - '8.3'
+          - '8.4'
         symfony-version:
           - '5.4.*'
           - '6.0.*'
@@ -45,6 +46,8 @@ jobs:
             symfony-version: '7.0.*'
           - php-version: '8.1'
             symfony-version: '7.1.*'
+          - php-version: '8.4'
+            dependencies: 'lowest'
         include:
           - php-version: '8.0'
             symfony-version: '5.4.*'
diff --git a/.php-cs-fixer.dist.php b/.php-cs-fixer.dist.php
index 8e9b5364a..bbb3b0d9b 100644
--- a/.php-cs-fixer.dist.php
+++ b/.php-cs-fixer.dist.php
@@ -35,6 +35,7 @@
             'single_line_comment_style' => false,
             'phpdoc_no_alias_tag' => ['replacements' => ['type' => 'var']],
             'no_mixed_echo_print' => ['use' => 'echo'],
+            'nullable_type_declaration_for_default_null_value' => true,
         ]
     )
     ->setFinder($finder)
diff --git a/src/Annotation/Builder.php b/src/Annotation/Builder.php
index beeb1d066..cb5003f4f 100644
--- a/src/Annotation/Builder.php
+++ b/src/Annotation/Builder.php
@@ -20,7 +20,7 @@ abstract class Builder extends Annotation
     /**
      * Builder name.
      */
-    public string $name;
+    public ?string $name;
 
     /**
      * The builder config.
@@ -31,7 +31,7 @@ abstract class Builder extends Annotation
      * @param string|null $name   The name of the builder
      * @param array       $config The builder configuration array
      */
-    public function __construct(string $name = null, array $config = [])
+    public function __construct(?string $name = null, array $config = [])
     {
         $this->name = $name;
         $this->config = $config;
diff --git a/src/Annotation/Input.php b/src/Annotation/Input.php
index cdbf0e936..9b18f8b94 100644
--- a/src/Annotation/Input.php
+++ b/src/Annotation/Input.php
@@ -27,7 +27,7 @@ final class Input extends Annotation
      */
     public bool $isRelay = false;
 
-    public function __construct(string $name = null, bool $isRelay = false)
+    public function __construct(?string $name = null, bool $isRelay = false)
     {
         $this->name = $name;
         $this->isRelay = $isRelay;
diff --git a/src/Annotation/Provider.php b/src/Annotation/Provider.php
index 6afd4a618..156b65d6c 100644
--- a/src/Annotation/Provider.php
+++ b/src/Annotation/Provider.php
@@ -37,11 +37,11 @@ final class Provider extends Annotation
     public ?array $targetMutationTypes;
 
     /**
-     * @param string               $prefix              A prefix to apply to the name of fields generated by this provider
+     * @param string|null          $prefix              A prefix to apply to the name of fields generated by this provider
      * @param string|string[]|null $targetQueryTypes    A list of GraphQL types to add the resolver queries to
      * @param string|string[]|null $targetMutationTypes A list of GraphQL types to add the resolver mutations to
      */
-    public function __construct(string $prefix = null, $targetQueryTypes = null, $targetMutationTypes = null)
+    public function __construct(?string $prefix = null, $targetQueryTypes = null, $targetMutationTypes = null)
     {
         $this->prefix = $prefix;
         $this->targetQueryTypes = is_string($targetQueryTypes) ? [$targetQueryTypes] : $targetQueryTypes;
diff --git a/src/Annotation/Relay/Connection.php b/src/Annotation/Relay/Connection.php
index e97174b13..4d20c0143 100644
--- a/src/Annotation/Relay/Connection.php
+++ b/src/Annotation/Relay/Connection.php
@@ -29,7 +29,7 @@ final class Connection extends Type
      */
     public ?string $node;
 
-    public function __construct(string $edge = null, string $node = null)
+    public function __construct(?string $edge = null, ?string $node = null)
     {
         $this->edge = $edge;
         $this->node = $node;
diff --git a/src/Annotation/Scalar.php b/src/Annotation/Scalar.php
index 13c2db6ca..6c2e7175c 100644
--- a/src/Annotation/Scalar.php
+++ b/src/Annotation/Scalar.php
@@ -25,7 +25,7 @@ final class Scalar extends Annotation
      * @param string|null $name       The GraphQL name of the Scalar
      * @param string|null $scalarType Expression to reuse an other scalar type
      */
-    public function __construct(string $name = null, string $scalarType = null)
+    public function __construct(?string $name = null, ?string $scalarType = null)
     {
         $this->name = $name;
         $this->scalarType = $scalarType;
diff --git a/src/Annotation/Type.php b/src/Annotation/Type.php
index e731f627e..7483a5b0a 100644
--- a/src/Annotation/Type.php
+++ b/src/Annotation/Type.php
@@ -52,11 +52,11 @@ class Type extends Annotation
      * @param string|null          $isTypeOf     An expression to resolve if the field is of given type
      */
     public function __construct(
-        string $name = null,
+        ?string $name = null,
         array $interfaces = [],
         bool $isRelay = false,
-        string $resolveField = null,
-        string $isTypeOf = null
+        ?string $resolveField = null,
+        ?string $isTypeOf = null
     ) {
         $this->name = $name;
         $this->interfaces = $interfaces;
diff --git a/src/Annotation/TypeInterface.php b/src/Annotation/TypeInterface.php
index f92bd3853..cd6af4ae1 100644
--- a/src/Annotation/TypeInterface.php
+++ b/src/Annotation/TypeInterface.php
@@ -28,7 +28,7 @@ final class TypeInterface extends Annotation
     public ?string $name;
 
     /**
-     * @param string        $resolveType The express resolve type
+     * @param string|null   $resolveType The express resolve type
      * @param string|null   $name        The GraphQL name of the interface
      */
     public function __construct(?string $resolveType = null, ?string $name = null)
diff --git a/src/Annotation/Union.php b/src/Annotation/Union.php
index dd32b3c45..c33d1a1eb 100644
--- a/src/Annotation/Union.php
+++ b/src/Annotation/Union.php
@@ -37,7 +37,7 @@ final class Union extends Annotation
      * @param string[]    $types       List of types included in the union
      * @param string|null $resolveType The resolve type expression
      */
-    public function __construct(string $name = null, array $types = [], ?string $resolveType = null)
+    public function __construct(?string $name = null, array $types = [], ?string $resolveType = null)
     {
         $this->name = $name;
         $this->types = $types;
diff --git a/src/CacheWarmer/CompileCacheWarmer.php b/src/CacheWarmer/CompileCacheWarmer.php
index e23f17c2a..ebfcac4be 100644
--- a/src/CacheWarmer/CompileCacheWarmer.php
+++ b/src/CacheWarmer/CompileCacheWarmer.php
@@ -29,7 +29,7 @@ public function isOptional(): bool
     /**
      * @return string[]
      */
-    public function warmUp(string $cacheDir, string $buildDir = null): array
+    public function warmUp(string $cacheDir, ?string $buildDir = null): array
     {
         if ($this->compiled) {
             // use warm up cache dir if type generator cache dir not already explicitly declared
diff --git a/src/Config/Processor/InheritanceProcessor.php b/src/Config/Processor/InheritanceProcessor.php
index 2e73edd9e..32c3da62a 100644
--- a/src/Config/Processor/InheritanceProcessor.php
+++ b/src/Config/Processor/InheritanceProcessor.php
@@ -124,7 +124,7 @@ private static function flattenInherits(
         string $name,
         array $configs,
         array $allowedTypes,
-        string $child = null,
+        ?string $child = null,
         array $typesTreated = []
     ): array {
         self::checkTypeExists($name, $configs, $child);
diff --git a/src/Controller/GraphController.php b/src/Controller/GraphController.php
index 95fd0991a..f1985ab6b 100644
--- a/src/Controller/GraphController.php
+++ b/src/Controller/GraphController.php
@@ -38,7 +38,7 @@ public function __construct(
     /**
      * @return JsonResponse|Response
      */
-    public function endpointAction(Request $request, string $schemaName = null)
+    public function endpointAction(Request $request, ?string $schemaName = null)
     {
         return $this->createResponse($request, $schemaName, false);
     }
@@ -46,7 +46,7 @@ public function endpointAction(Request $request, string $schemaName = null)
     /**
      * @return JsonResponse|Response
      */
-    public function batchEndpointAction(Request $request, string $schemaName = null)
+    public function batchEndpointAction(Request $request, ?string $schemaName = null)
     {
         return $this->createResponse($request, $schemaName, true);
     }
@@ -92,7 +92,7 @@ private function processQuery(Request $request, ?string $schemaName, bool $batch
         return $payload;
     }
 
-    private function processBatchQuery(Request $request, string $schemaName = null): array
+    private function processBatchQuery(Request $request, ?string $schemaName = null): array
     {
         $queries = $this->batchParser->parse($request);
         $payloads = [];
@@ -110,7 +110,7 @@ private function processBatchQuery(Request $request, string $schemaName = null):
         return $payloads;
     }
 
-    private function processNormalQuery(Request $request, string $schemaName = null): array
+    private function processNormalQuery(Request $request, ?string $schemaName = null): array
     {
         $params = $this->requestParser->parse($request);
 
diff --git a/src/DataCollector/GraphQLCollector.php b/src/DataCollector/GraphQLCollector.php
index c9ac7c3a2..577b9b14f 100644
--- a/src/DataCollector/GraphQLCollector.php
+++ b/src/DataCollector/GraphQLCollector.php
@@ -25,7 +25,7 @@ final class GraphQLCollector extends DataCollector
      */
     protected array $batches = [];
 
-    public function collect(Request $request, Response $response, Throwable $exception = null): void
+    public function collect(Request $request, Response $response, ?Throwable $exception = null): void
     {
         $error = false;
         $count = 0;
diff --git a/src/Definition/Argument.php b/src/Definition/Argument.php
index 8c16deb60..ba446e5bc 100644
--- a/src/Definition/Argument.php
+++ b/src/Definition/Argument.php
@@ -11,12 +11,12 @@ final class Argument implements ArgumentInterface
 {
     private array $rawArguments = [];
 
-    public function __construct(array $rawArguments = null)
+    public function __construct(?array $rawArguments = null)
     {
         $this->exchangeArray($rawArguments);
     }
 
-    public function exchangeArray(array $array = null): array
+    public function exchangeArray(?array $array = null): array
     {
         $old = $this->rawArguments;
         $this->rawArguments = $array ?? [];
diff --git a/src/Definition/Builder/SchemaBuilder.php b/src/Definition/Builder/SchemaBuilder.php
index aee461512..dc3482bd1 100644
--- a/src/Definition/Builder/SchemaBuilder.php
+++ b/src/Definition/Builder/SchemaBuilder.php
@@ -23,7 +23,7 @@ public function __construct(TypeResolver $typeResolver, bool $enableValidation =
         $this->enableValidation = $enableValidation;
     }
 
-    public function getBuilder(string $name, ?string $queryAlias, string $mutationAlias = null, string $subscriptionAlias = null, array $types = []): Closure
+    public function getBuilder(string $name, ?string $queryAlias, ?string $mutationAlias = null, ?string $subscriptionAlias = null, array $types = []): Closure
     {
         return function () use ($name, $queryAlias, $mutationAlias, $subscriptionAlias, $types): ExtensibleSchema {
             static $schema = null;
@@ -38,7 +38,7 @@ public function getBuilder(string $name, ?string $queryAlias, string $mutationAl
     /**
      * @param string[] $types
      */
-    public function create(string $name, ?string $queryAlias, string $mutationAlias = null, string $subscriptionAlias = null, array $types = []): ExtensibleSchema
+    public function create(string $name, ?string $queryAlias, ?string $mutationAlias = null, ?string $subscriptionAlias = null, array $types = []): ExtensibleSchema
     {
         $this->typeResolver->setCurrentSchemaName($name);
         $query = $this->typeResolver->resolve($queryAlias);
diff --git a/src/Definition/Type/CustomScalarType.php b/src/Definition/Type/CustomScalarType.php
index c1858b873..1fb09c2cb 100644
--- a/src/Definition/Type/CustomScalarType.php
+++ b/src/Definition/Type/CustomScalarType.php
@@ -63,7 +63,7 @@ public function parseValue($value): mixed
     /**
      * {@inheritdoc}
      */
-    public function parseLiteral(/* GraphQL\Language\AST\ValueNode */ $valueNode, array $variables = null): mixed
+    public function parseLiteral(/* GraphQL\Language\AST\ValueNode */ $valueNode, ?array $variables = null): mixed
     {
         return $this->call('parseLiteral', $valueNode);
     }
diff --git a/src/Definition/Type/PhpEnumType.php b/src/Definition/Type/PhpEnumType.php
index 21e0f4452..dcdaf72b0 100644
--- a/src/Definition/Type/PhpEnumType.php
+++ b/src/Definition/Type/PhpEnumType.php
@@ -93,7 +93,7 @@ public function parseValue($value): mixed
         return parent::parseValue($value);
     }
 
-    public function parseLiteral(Node $valueNode, array $variables = null): mixed
+    public function parseLiteral(Node $valueNode, ?array $variables = null): mixed
     {
         if ($this->enumClass) {
             if (!$valueNode instanceof EnumValueNode) {
diff --git a/src/DependencyInjection/Compiler/ConfigParserPass.php b/src/DependencyInjection/Compiler/ConfigParserPass.php
index e23e55211..3d5ecd308 100644
--- a/src/DependencyInjection/Compiler/ConfigParserPass.php
+++ b/src/DependencyInjection/Compiler/ConfigParserPass.php
@@ -240,7 +240,7 @@ private function mappingFromBundles(ContainerBuilder $container): array
         return $typesMappings;
     }
 
-    private function detectFilesByTypes(ContainerBuilder $container, string $path, string $suffix, array $types = null): array
+    private function detectFilesByTypes(ContainerBuilder $container, string $path, string $suffix, ?array $types = null): array
     {
         // add the closest existing directory as a resource
         $resource = $path;
diff --git a/src/Error/InvalidArgumentError.php b/src/Error/InvalidArgumentError.php
index 793b288db..5f17e63c3 100644
--- a/src/Error/InvalidArgumentError.php
+++ b/src/Error/InvalidArgumentError.php
@@ -18,7 +18,7 @@ public function __construct(
         ConstraintViolationListInterface $errors,
         string $message = '',
         int $code = 0,
-        Exception $previous = null
+        ?Exception $previous = null
     ) {
         $this->name = $name;
         $this->errors = $errors;
diff --git a/src/Error/InvalidArgumentsError.php b/src/Error/InvalidArgumentsError.php
index 93168041b..a9a450e88 100644
--- a/src/Error/InvalidArgumentsError.php
+++ b/src/Error/InvalidArgumentsError.php
@@ -16,7 +16,7 @@ public function __construct(
         array $errors,
         string $message = '',
         int $code = 0,
-        Exception $previous = null
+        ?Exception $previous = null
     ) {
         $this->errors = $errors;
         parent::__construct($message, $code, $previous);
diff --git a/src/Error/UserErrors.php b/src/Error/UserErrors.php
index 426145ce7..66e4a3f42 100644
--- a/src/Error/UserErrors.php
+++ b/src/Error/UserErrors.php
@@ -22,7 +22,7 @@ public function __construct(
         array $errors,
         string $message = '',
         int $code = 0,
-        Exception $previous = null
+        ?Exception $previous = null
     ) {
         $this->setErrors($errors);
         parent::__construct($message, $code, $previous);
diff --git a/src/Event/ExecutorArgumentsEvent.php b/src/Event/ExecutorArgumentsEvent.php
index ffe6096a5..f6c708b5e 100644
--- a/src/Event/ExecutorArgumentsEvent.php
+++ b/src/Event/ExecutorArgumentsEvent.php
@@ -30,8 +30,8 @@ public static function create(
         string $requestString,
         ArrayObject $contextValue,
         mixed $rootValue = null,
-        array $variableValue = null,
-        string $operationName = null
+        ?array $variableValue = null,
+        ?string $operationName = null
     ): self {
         $instance = new self();
         $instance->setSchemaName($schemaName);
diff --git a/src/EventListener/ErrorLoggerListener.php b/src/EventListener/ErrorLoggerListener.php
index efbd62ad8..4c3670667 100644
--- a/src/EventListener/ErrorLoggerListener.php
+++ b/src/EventListener/ErrorLoggerListener.php
@@ -20,7 +20,7 @@ final class ErrorLoggerListener
 
     private LoggerInterface $logger;
 
-    public function __construct(LoggerInterface $logger = null)
+    public function __construct(?LoggerInterface $logger = null)
     {
         $this->logger = $logger ?? new NullLogger();
     }
diff --git a/src/Executor/Executor.php b/src/Executor/Executor.php
index 6294b1bb1..222d3c6a7 100644
--- a/src/Executor/Executor.php
+++ b/src/Executor/Executor.php
@@ -28,8 +28,8 @@ public function execute(
         $contextValue = null,
         $variableValues = null,
         $operationName = null,
-        callable $fieldResolver = null,
-        array $validationRules = null
+        ?callable $fieldResolver = null,
+        ?array $validationRules = null
     ): ExecutionResult {
         if (!method_exists($promiseAdapter, 'wait')) {
             throw new RuntimeException(
diff --git a/src/Executor/ExecutorInterface.php b/src/Executor/ExecutorInterface.php
index 22240abf1..0cd6ec452 100644
--- a/src/Executor/ExecutorInterface.php
+++ b/src/Executor/ExecutorInterface.php
@@ -25,7 +25,7 @@ public function execute(
         $contextValue = null,
         $variableValues = null,
         $operationName = null,
-        callable $fieldResolver = null,
-        array $validationRules = null
+        ?callable $fieldResolver = null,
+        ?array $validationRules = null
     ): ExecutionResult;
 }
diff --git a/src/Executor/Promise/Adapter/ReactPromiseAdapter.php b/src/Executor/Promise/Adapter/ReactPromiseAdapter.php
index e09c49c8f..05ffa478a 100644
--- a/src/Executor/Promise/Adapter/ReactPromiseAdapter.php
+++ b/src/Executor/Promise/Adapter/ReactPromiseAdapter.php
@@ -42,7 +42,7 @@ public function convertThenable($thenable): Promise
      *
      * @throws Exception
      */
-    public function wait(Promise $promise, callable $onProgress = null): ?ExecutionResult
+    public function wait(Promise $promise, ?callable $onProgress = null): ?ExecutionResult
     {
         if (!$this->isThenable($promise)) {
             throw new InvalidArgumentException(sprintf('The "%s" method must be call with compatible a Promise.', __METHOD__));
diff --git a/src/ExpressionLanguage/Exception/EvaluatorIsNotAllowedException.php b/src/ExpressionLanguage/Exception/EvaluatorIsNotAllowedException.php
index 58d23de12..be4053c84 100644
--- a/src/ExpressionLanguage/Exception/EvaluatorIsNotAllowedException.php
+++ b/src/ExpressionLanguage/Exception/EvaluatorIsNotAllowedException.php
@@ -9,7 +9,7 @@
 
 final class EvaluatorIsNotAllowedException extends Exception
 {
-    public function __construct(string $expressionFunctionName, int $code = 0, Throwable $previous = null)
+    public function __construct(string $expressionFunctionName, int $code = 0, ?Throwable $previous = null)
     {
         parent::__construct(
             "The expression function '$expressionFunctionName' cannot be used by it's evaluator.",
diff --git a/src/ExpressionLanguage/ExpressionFunction.php b/src/ExpressionLanguage/ExpressionFunction.php
index 5bd965ee8..06b9610ff 100644
--- a/src/ExpressionLanguage/ExpressionFunction.php
+++ b/src/ExpressionLanguage/ExpressionFunction.php
@@ -12,7 +12,7 @@ class ExpressionFunction extends BaseExpressionFunction
 {
     protected string $gqlServices = '$'.TypeGenerator::GRAPHQL_SERVICES;
 
-    public function __construct(string $name, callable $compiler, callable $evaluator = null)
+    public function __construct(string $name, callable $compiler, ?callable $evaluator = null)
     {
         if (null === $evaluator) {
             $evaluator = new EvaluatorIsNotAllowedException($name);
diff --git a/src/ExpressionLanguage/ExpressionFunction/GraphQL/Relay/GlobalID.php b/src/ExpressionLanguage/ExpressionFunction/GraphQL/Relay/GlobalID.php
index 4c923500b..4f41042c2 100644
--- a/src/ExpressionLanguage/ExpressionFunction/GraphQL/Relay/GlobalID.php
+++ b/src/ExpressionLanguage/ExpressionFunction/GraphQL/Relay/GlobalID.php
@@ -15,7 +15,7 @@ public function __construct()
     {
         parent::__construct(
             'globalId',
-            function (string $id, string $typeName = null): string {
+            function (string $id, ?string $typeName = null): string {
                 $typeName = $this->isTypeNameEmpty($typeName) ? '$info->parentType->name' : $typeName;
 
                 return sprintf('\%s::toGlobalId(%s, %s)', GlobalIdHelper::class, $typeName, $id);
diff --git a/src/Generator/TypeBuilder.php b/src/Generator/TypeBuilder.php
index 5eb64041c..6952abeaf 100644
--- a/src/Generator/TypeBuilder.php
+++ b/src/Generator/TypeBuilder.php
@@ -449,7 +449,7 @@ private function buildScalarCallback($callback, string $fieldName)
      *
      * @throws GeneratorException
      */
-    private function buildResolve($resolve, array $groups = null): GeneratorInterface
+    private function buildResolve($resolve, ?array $groups = null): GeneratorInterface
     {
         if (is_callable($resolve) && is_array($resolve)) {
             return Collection::numeric($resolve);
diff --git a/src/Generator/TypeGeneratorOptions.php b/src/Generator/TypeGeneratorOptions.php
index 14ae5df19..54b65bfae 100644
--- a/src/Generator/TypeGeneratorOptions.php
+++ b/src/Generator/TypeGeneratorOptions.php
@@ -36,8 +36,8 @@ public function __construct(
         string $namespace,
         ?string $cacheDir,
         bool $useClassMap = true,
-        string $cacheBaseDir = null,
-        int $cacheDirMask = null
+        ?string $cacheBaseDir = null,
+        ?int $cacheDirMask = null
     ) {
         $this->namespace = $namespace;
         $this->cacheDir = $cacheDir;
diff --git a/src/Relay/Connection/ConnectionBuilder.php b/src/Relay/Connection/ConnectionBuilder.php
index 629624ea3..d0b701762 100644
--- a/src/Relay/Connection/ConnectionBuilder.php
+++ b/src/Relay/Connection/ConnectionBuilder.php
@@ -59,7 +59,7 @@ final class ConnectionBuilder
      * @phpstan-param ConnectionFactoryFunc|null $connectionCallback
      * @phpstan-param EdgeFactoryFunc|null $edgeCallback
      */
-    public function __construct(CursorEncoderInterface $cursorEncoder = null, callable $connectionCallback = null, callable $edgeCallback = null)
+    public function __construct(?CursorEncoderInterface $cursorEncoder = null, ?callable $connectionCallback = null, ?callable $edgeCallback = null)
     {
         $this->cursorEncoder = $cursorEncoder ?? new Base64CursorEncoder();
         $this->connectionCallback = $connectionCallback ?? static fn (array $edges, PageInfoInterface $pageInfo): Connection => new Connection($edges, $pageInfo);
diff --git a/src/Relay/Connection/Output/Connection.php b/src/Relay/Connection/Output/Connection.php
index ce36a6dd4..d3fa1f739 100644
--- a/src/Relay/Connection/Output/Connection.php
+++ b/src/Relay/Connection/Output/Connection.php
@@ -31,7 +31,7 @@ class Connection implements ConnectionInterface
     /**
      * @param EdgeInterface<T>[] $edges
      */
-    public function __construct(array $edges = [], PageInfoInterface $pageInfo = null)
+    public function __construct(array $edges = [], ?PageInfoInterface $pageInfo = null)
     {
         $this->edges = $edges;
         $this->pageInfo = $pageInfo;
diff --git a/src/Relay/Connection/Output/Edge.php b/src/Relay/Connection/Output/Edge.php
index ad4f1c9da..295829c2e 100644
--- a/src/Relay/Connection/Output/Edge.php
+++ b/src/Relay/Connection/Output/Edge.php
@@ -25,7 +25,7 @@ class Edge implements EdgeInterface
      *
      * @phpstan-param T|null $node
      */
-    public function __construct(string $cursor = null, $node = null)
+    public function __construct(?string $cursor = null, $node = null)
     {
         $this->cursor = $cursor;
         $this->node = $node;
diff --git a/src/Relay/Connection/Output/PageInfo.php b/src/Relay/Connection/Output/PageInfo.php
index da9a5b999..40f522ea3 100644
--- a/src/Relay/Connection/Output/PageInfo.php
+++ b/src/Relay/Connection/Output/PageInfo.php
@@ -15,7 +15,7 @@ final class PageInfo implements PageInfoInterface
     protected ?bool $hasPreviousPage;
     protected ?bool $hasNextPage;
 
-    public function __construct(string $startCursor = null, string $endCursor = null, bool $hasPreviousPage = null, bool $hasNextPage = null)
+    public function __construct(?string $startCursor = null, ?string $endCursor = null, ?bool $hasPreviousPage = null, ?bool $hasNextPage = null)
     {
         $this->startCursor = $startCursor;
         $this->endCursor = $endCursor;
diff --git a/src/Relay/Connection/Paginator.php b/src/Relay/Connection/Paginator.php
index 90ab63ff8..e7f810d92 100644
--- a/src/Relay/Connection/Paginator.php
+++ b/src/Relay/Connection/Paginator.php
@@ -27,7 +27,7 @@ final class Paginator
     /** @var callable */
     private $fetcher;
 
-    public function __construct(callable $fetcher, bool $promise = self::MODE_REGULAR, ConnectionBuilder $connectionBuilder = null)
+    public function __construct(callable $fetcher, bool $promise = self::MODE_REGULAR, ?ConnectionBuilder $connectionBuilder = null)
     {
         $this->fetcher = $fetcher;
         $this->promise = $promise;
diff --git a/src/Request/Executor.php b/src/Request/Executor.php
index 706cd4fa1..e6af42b84 100644
--- a/src/Request/Executor.php
+++ b/src/Request/Executor.php
@@ -44,7 +44,7 @@ public function __construct(
         ExecutorInterface $executor,
         PromiseAdapter $promiseAdapter,
         EventDispatcherInterface $dispatcher,
-        callable $defaultFieldResolver = null
+        ?callable $defaultFieldResolver = null
     ) {
         $this->executor = $executor;
         $this->promiseAdapter = $promiseAdapter;
@@ -73,7 +73,7 @@ public function addSchema(string $name, Schema $schema): self
         return $this;
     }
 
-    public function getSchema(string $name = null): Schema
+    public function getSchema(?string $name = null): Schema
     {
         if (empty($this->schemas)) {
             throw new RuntimeException('At least one schema should be declare.');
@@ -171,8 +171,8 @@ private function preExecute(
         string $requestString,
         ArrayObject $contextValue,
         $rootValue = null,
-        array $variableValue = null,
-        string $operationName = null
+        ?array $variableValue = null,
+        ?string $operationName = null
     ): ExecutorArgumentsEvent {
         // @phpstan-ignore-next-line (only for Symfony 4.4)
         $this->dispatcher->dispatch(new ExecutorContextEvent($contextValue), Events::EXECUTOR_CONTEXT);
diff --git a/src/Resolver/AccessResolver.php b/src/Resolver/AccessResolver.php
index 187a2e25c..c73f95e6c 100644
--- a/src/Resolver/AccessResolver.php
+++ b/src/Resolver/AccessResolver.php
@@ -138,7 +138,7 @@ private function extractAdoptedPromise($object)
     /**
      * @param mixed $promise
      */
-    private function createPromise($promise, callable $onFulfilled = null): Promise
+    private function createPromise($promise, ?callable $onFulfilled = null): Promise
     {
         return $this->promiseAdapter->then(
             new Promise($this->extractAdoptedPromise($promise), $this->promiseAdapter),
diff --git a/src/Resolver/ResolverMap.php b/src/Resolver/ResolverMap.php
index 816c0da69..497ec86ea 100644
--- a/src/Resolver/ResolverMap.php
+++ b/src/Resolver/ResolverMap.php
@@ -70,7 +70,7 @@ public function isResolvable(string $typeName, string $fieldName): bool
     /**
      * {@inheritdoc}
      */
-    public function covered(string $typeName = null)
+    public function covered(?string $typeName = null)
     {
         $loadedMap = $this->getLoadedMap();
         $covered = [];
diff --git a/src/Resolver/ResolverMapInterface.php b/src/Resolver/ResolverMapInterface.php
index c6938b46e..6dd99ccda 100644
--- a/src/Resolver/ResolverMapInterface.php
+++ b/src/Resolver/ResolverMapInterface.php
@@ -42,5 +42,5 @@ public function isResolvable(string $typeName, string $fieldName): bool;
      *
      * @return array
      */
-    public function covered(string $typeName = null);
+    public function covered(?string $typeName = null);
 }
diff --git a/src/Resolver/ResolverMaps.php b/src/Resolver/ResolverMaps.php
index c2b60510e..be838adc3 100644
--- a/src/Resolver/ResolverMaps.php
+++ b/src/Resolver/ResolverMaps.php
@@ -52,7 +52,7 @@ public function isResolvable(string $typeName, string $fieldName): bool
     /**
      * {@inheritdoc}
      */
-    public function covered(string $typeName = null)
+    public function covered(?string $typeName = null)
     {
         $covered = [];
         foreach ($this->resolverMaps as $resolverMap) {
diff --git a/src/Transformer/ArgumentsTransformer.php b/src/Transformer/ArgumentsTransformer.php
index c653d881a..12fce60a7 100644
--- a/src/Transformer/ArgumentsTransformer.php
+++ b/src/Transformer/ArgumentsTransformer.php
@@ -34,7 +34,7 @@ final class ArgumentsTransformer
     private ?ValidatorInterface $validator;
     private array $classesMap;
 
-    public function __construct(ValidatorInterface $validator = null, array $classesMap = [])
+    public function __construct(?ValidatorInterface $validator = null, array $classesMap = [])
     {
         $this->validator = $validator;
         $this->accessor = PropertyAccess::createPropertyAccessor();
diff --git a/src/Upload/Type/GraphQLUploadType.php b/src/Upload/Type/GraphQLUploadType.php
index 7a4d30ec0..8f493dd7d 100644
--- a/src/Upload/Type/GraphQLUploadType.php
+++ b/src/Upload/Type/GraphQLUploadType.php
@@ -14,7 +14,7 @@
 
 final class GraphQLUploadType extends ScalarType
 {
-    public function __construct(string $name = null)
+    public function __construct(?string $name = null)
     {
         parent::__construct([
             'name' => $name,
@@ -52,7 +52,7 @@ public function serialize($value): void
     /**
      * {@inheritdoc}
      */
-    public function parseLiteral($valueNode, array $variables = null): void
+    public function parseLiteral($valueNode, ?array $variables = null): void
     {
         throw new InvariantViolation(sprintf('%s scalar literal unsupported.', $this->name));
     }
diff --git a/src/Validator/Exception/ArgumentsValidationException.php b/src/Validator/Exception/ArgumentsValidationException.php
index fca5e611b..92ed7f8bf 100644
--- a/src/Validator/Exception/ArgumentsValidationException.php
+++ b/src/Validator/Exception/ArgumentsValidationException.php
@@ -13,7 +13,7 @@ final class ArgumentsValidationException extends Exception implements ClientAwar
 {
     private ConstraintViolationListInterface $violations;
 
-    public function __construct(ConstraintViolationListInterface $violations, Throwable $previous = null)
+    public function __construct(ConstraintViolationListInterface $violations, ?Throwable $previous = null)
     {
         $this->violations = $violations;
         parent::__construct('validation', 0, $previous);
diff --git a/src/Validator/InputValidator.php b/src/Validator/InputValidator.php
index 18846c393..8059456ed 100644
--- a/src/Validator/InputValidator.php
+++ b/src/Validator/InputValidator.php
@@ -63,7 +63,7 @@ public function __construct(
     /**
      * @throws ArgumentsValidationException
      */
-    public function validate(string|array $groups = null, bool $throw = true): ?ConstraintViolationListInterface
+    public function validate(string|array|null $groups = null, bool $throw = true): ?ConstraintViolationListInterface
     {
         $rootNode = new ValidationNode(
             $this->info->parentType,
diff --git a/src/Validator/ValidationNode.php b/src/Validator/ValidationNode.php
index a13d3848a..7a0c39b56 100644
--- a/src/Validator/ValidationNode.php
+++ b/src/Validator/ValidationNode.php
@@ -50,9 +50,9 @@ final class ValidationNode
 
     public function __construct(
         ObjectType|InputObjectType $type,
-        string $field = null,
-        ValidationNode $parent = null,
-        ResolverArgs $resolverArgs = null
+        ?string $field = null,
+        ?ValidationNode $parent = null,
+        ?ResolverArgs $resolverArgs = null
     ) {
         $this->__type = $type;
         $this->__fieldName = $field;
diff --git a/tests/Config/Parser/fixtures/annotations/Type/Battle.php b/tests/Config/Parser/fixtures/annotations/Type/Battle.php
index 30be8b833..678277975 100644
--- a/tests/Config/Parser/fixtures/annotations/Type/Battle.php
+++ b/tests/Config/Parser/fixtures/annotations/Type/Battle.php
@@ -29,12 +29,12 @@ final class Battle
     public function getCasualties(
         int $areaId,
         ?string $raceId,
-        int $dayStart = null,
-        int $dayEnd = null,
+        ?int $dayStart = null,
+        ?int $dayEnd = null,
         string $nameStartingWith = '',
-        Planet $planet = null,
+        ?Planet $planet = null,
         bool $away = false,
-        float $maxDistance = null
+        ?float $maxDistance = null
     ): ?int {
         return 12;
     }
diff --git a/tests/DependencyInjection/Builder/TimestampFields.php b/tests/DependencyInjection/Builder/TimestampFields.php
index bcfdff2f9..4878df0bb 100644
--- a/tests/DependencyInjection/Builder/TimestampFields.php
+++ b/tests/DependencyInjection/Builder/TimestampFields.php
@@ -8,7 +8,7 @@
 
 final class TimestampFields implements MappingInterface
 {
-    public function toMappingDefinition(array $config = null): array
+    public function toMappingDefinition(?array $config = null): array
     {
         return [
             'createdAt' => [
diff --git a/tests/DependencyInjection/Compiler/ConfigParserPassTest.php b/tests/DependencyInjection/Compiler/ConfigParserPassTest.php
index 7ce3e90d1..ff20a7fe9 100644
--- a/tests/DependencyInjection/Compiler/ConfigParserPassTest.php
+++ b/tests/DependencyInjection/Compiler/ConfigParserPassTest.php
@@ -564,7 +564,7 @@ public function fieldBuilderTypeOverrideNotAllowedProvider(): array
         ];
     }
 
-    private function processCompilerPass(array $configs, ConfigParserPass $compilerPass = null, ContainerBuilder $container = null): void
+    private function processCompilerPass(array $configs, ?ConfigParserPass $compilerPass = null, ?ContainerBuilder $container = null): void
     {
         $container ??= $this->container;
         $compilerPass ??= $this->compilerPass;
diff --git a/tests/EventListener/TypeDecoratorListenerTest.php b/tests/EventListener/TypeDecoratorListenerTest.php
index ccd07160a..ccfbf74b8 100644
--- a/tests/EventListener/TypeDecoratorListenerTest.php
+++ b/tests/EventListener/TypeDecoratorListenerTest.php
@@ -33,7 +33,7 @@ final class TypeDecoratorListenerTest extends TestCase
      *
      * @dataProvider specialTypeFieldProvider
      */
-    public function testSpecialField($fieldName, ObjectType|UnionType|InterfaceType|CustomScalarType $typeWithSpecialField, callable $fieldValueRetriever = null, $strict = true): void
+    public function testSpecialField($fieldName, ObjectType|UnionType|InterfaceType|CustomScalarType $typeWithSpecialField, ?callable $fieldValueRetriever = null, $strict = true): void
     {
         if (null === $fieldValueRetriever) {
             $fieldValueRetriever = fn (ObjectType|UnionType|InterfaceType|CustomScalarType $type, $fieldName) => $type->config[$fieldName];
@@ -292,12 +292,12 @@ public function specialTypeFieldProvider(): array
             // custom scalar
             [ResolverMapInterface::SERIALIZE, new CustomScalarType(['name' => 'Custom', 'scalarType' => Type::string(), 'serialize' => fn (mixed $input): mixed => ''])],
             [ResolverMapInterface::PARSE_VALUE, new CustomScalarType(['name' => 'Custom', 'scalarType' => Type::string(), 'serialize' => fn (mixed $input): mixed => '', 'parseValue' => fn (mixed $input): mixed => ''])],
-            [ResolverMapInterface::PARSE_LITERAL, new CustomScalarType(['name' => 'Custom', 'scalarType' => Type::string(), 'serialize' => fn (mixed $input): mixed => '', 'parseLiteral' => fn (Node $a, array|null $b): mixed => ''])],
+            [ResolverMapInterface::PARSE_LITERAL, new CustomScalarType(['name' => 'Custom', 'scalarType' => Type::string(), 'serialize' => fn (mixed $input): mixed => '', 'parseLiteral' => fn (Node $a, ?array $b): mixed => ''])],
             [ResolverMapInterface::SCALAR_TYPE, new CustomScalarType(['name' => 'Custom', 'scalarType' => Type::string(), 'serialize' => fn (mixed $input): mixed => ''])],
         ];
     }
 
-    private function assertDecorateException(array $types, array $map, string $exception = null, string $exceptionMessage = null): void
+    private function assertDecorateException(array $types, array $map, ?string $exception = null, ?string $exceptionMessage = null): void
     {
         if ($exception) {
             $this->expectException($exception); // @phpstan-ignore-line
diff --git a/tests/ExpressionLanguage/ExpressionFunction/GraphQL/ArgumentsTest.php b/tests/ExpressionLanguage/ExpressionFunction/GraphQL/ArgumentsTest.php
index 5e24b1c21..ffa8996d8 100644
--- a/tests/ExpressionLanguage/ExpressionFunction/GraphQL/ArgumentsTest.php
+++ b/tests/ExpressionLanguage/ExpressionFunction/GraphQL/ArgumentsTest.php
@@ -44,7 +44,7 @@ public function getResolveInfo(array $types): ResolveInfo
         return $info;
     }
 
-    private function getTransformer(array $classesMap = null): ArgumentsTransformer
+    private function getTransformer(?array $classesMap = null): ArgumentsTransformer
     {
         $validator = $this->createMock(RecursiveValidator::class);
         $validator->method('validate')->willReturn(new ConstraintViolationList());
diff --git a/tests/ExpressionLanguage/TestCase.php b/tests/ExpressionLanguage/TestCase.php
index 0db2a43d1..43df70737 100644
--- a/tests/ExpressionLanguage/TestCase.php
+++ b/tests/ExpressionLanguage/TestCase.php
@@ -55,7 +55,7 @@ protected function assertExpressionCompile(
         $expression,
         $with,
         array $vars = [],
-        InvokedCount $expects = null,
+        ?InvokedCount $expects = null,
         bool $return = true,
         string $assertMethod = 'assertTrue'
     ): void {
diff --git a/tests/Functional/App/Mutation/InputValidatorMutation.php b/tests/Functional/App/Mutation/InputValidatorMutation.php
index 056917717..e4aee1c27 100644
--- a/tests/Functional/App/Mutation/InputValidatorMutation.php
+++ b/tests/Functional/App/Mutation/InputValidatorMutation.php
@@ -16,7 +16,7 @@ final class InputValidatorMutation implements MutationInterface
     /**
      * @throws ArgumentsValidationException
      */
-    public function mutationMock(Argument $args, InputValidator $validator = null): bool
+    public function mutationMock(Argument $args, ?InputValidator $validator = null): bool
     {
         if (null !== $validator) {
             $validator($args['groups']);
diff --git a/tests/Functional/App/TestKernel.php b/tests/Functional/App/TestKernel.php
index 3c2c5981f..6f5c6874d 100644
--- a/tests/Functional/App/TestKernel.php
+++ b/tests/Functional/App/TestKernel.php
@@ -31,7 +31,7 @@ public function registerBundles(): iterable
         yield new OverblogGraphQLBundle();
     }
 
-    public function __construct(string $environment, bool $debug, string $testCase = null)
+    public function __construct(string $environment, bool $debug, ?string $testCase = null)
     {
         $this->testCase = $testCase;
         parent::__construct($environment, $debug);
diff --git a/tests/Functional/App/Type/YearScalarType.php b/tests/Functional/App/Type/YearScalarType.php
index ffa1832b4..e2a215725 100644
--- a/tests/Functional/App/Type/YearScalarType.php
+++ b/tests/Functional/App/Type/YearScalarType.php
@@ -32,7 +32,7 @@ public function parseValue($value): mixed
     /**
      * {@inheritdoc}
      */
-    public function parseLiteral($valueNode, array $variables = null): mixed
+    public function parseLiteral($valueNode, ?array $variables = null): mixed
     {
         if (!$valueNode instanceof StringValueNode) {
             throw new Error('Query error: Can only parse strings got: '.$valueNode->kind, $valueNode);
diff --git a/tests/Functional/BaseTestCase.php b/tests/Functional/BaseTestCase.php
index 172e613b0..670c86386 100644
--- a/tests/Functional/BaseTestCase.php
+++ b/tests/Functional/BaseTestCase.php
@@ -71,7 +71,7 @@ protected function tearDown(): void
         static::ensureKernelShutdown();
     }
 
-    protected static function executeGraphQLRequest(string $query, array $rootValue = [], string $schemaName = null, array $variables = []): array
+    protected static function executeGraphQLRequest(string $query, array $rootValue = [], ?string $schemaName = null, array $variables = []): array
     {
         $request = new Request();
         $request->query->set('query', $query);
@@ -87,7 +87,7 @@ protected static function executeGraphQLRequest(string $query, array $rootValue
         return $res->toArray();
     }
 
-    protected static function assertGraphQL(string $query, array $expectedData = null, array $expectedErrors = null, array $rootValue = [], string $schemaName = null): void
+    protected static function assertGraphQL(string $query, ?array $expectedData = null, ?array $expectedErrors = null, array $rootValue = [], ?string $schemaName = null): void
     {
         $result = static::executeGraphQLRequest($query, $rootValue, $schemaName);
 
@@ -127,7 +127,7 @@ protected static function createClientAuthenticated(?string $username, string $t
         return $client;
     }
 
-    protected static function assertResponse(string $query, array $expected, ?string $username, string $testCase, ?string $password = self::DEFAULT_PASSWORD, array $variables = null): KernelBrowser
+    protected static function assertResponse(string $query, array $expected, ?string $username, string $testCase, ?string $password = self::DEFAULT_PASSWORD, ?array $variables = null): KernelBrowser
     {
         $client = self::createClientAuthenticated($username, $testCase, $password);
         $result = self::sendRequest($client, $query, false, $variables);
@@ -140,7 +140,7 @@ protected static function assertResponse(string $query, array $expected, ?string
     /**
      * @return mixed
      */
-    protected static function sendRequest(KernelBrowser $client, string $query, bool $isDecoded = false, array $variables = null)
+    protected static function sendRequest(KernelBrowser $client, string $query, bool $isDecoded = false, ?array $variables = null)
     {
         $client->request('GET', '/', ['query' => $query, 'variables' => json_encode($variables)]);
         $result = $client->getResponse()->getContent();
diff --git a/tests/Relay/Connection/ConnectionBuilderFromPromisedTest.php b/tests/Relay/Connection/ConnectionBuilderFromPromisedTest.php
index 3b02f6a54..7dc744761 100644
--- a/tests/Relay/Connection/ConnectionBuilderFromPromisedTest.php
+++ b/tests/Relay/Connection/ConnectionBuilderFromPromisedTest.php
@@ -87,7 +87,7 @@ public function testInvalidPromiseWhenSlicing($invalidPromise): void
     /**
      * @return ExtendedPromiseInterface|FulfilledPromise|Promise|PromiseInterface
      */
-    private function promisedLetters(array $letters = null)
+    private function promisedLetters(?array $letters = null)
     {
         return resolve($letters ?: $this->letters);
     }
diff --git a/tests/Transformer/ArgumentsTransformerTest.php b/tests/Transformer/ArgumentsTransformerTest.php
index 9ef2d3398..408d508ab 100644
--- a/tests/Transformer/ArgumentsTransformerTest.php
+++ b/tests/Transformer/ArgumentsTransformerTest.php
@@ -37,7 +37,7 @@ protected function setUp(): void
         }
     }
 
-    private function getTransformer(array $classesMap = [], ConstraintViolationList $validateReturn = null): ArgumentsTransformer
+    private function getTransformer(array $classesMap = [], ?ConstraintViolationList $validateReturn = null): ArgumentsTransformer
     {
         $validator = $this->createMock(RecursiveValidator::class);
         $validator->method('validate')->willReturn($validateReturn ?? new ConstraintViolationList());