Fix implicit nullable parameter (#977)

| Q               | A
| --------------- | -----
| Bug fix?        | yes (fix deprecations)
| New feature?    | no
| BC breaks?      | no
| Deprecations?   | no
| Related tickets | 
| License         | MIT

Bc-layer seems ok
https://3v4l.org/s8Mv1
https://3v4l.org/TastR

Author: GSadee

src/Bundle/Controller/ControllerTrait.php

@@ -143,7 +143,7 @@ protected function json($data, int $status = 200, array $headers = [], array $co
      *
      * @final
      */
-    protected function file($file, string $fileName = null, string $disposition = ResponseHeaderBag::DISPOSITION_ATTACHMENT): BinaryFileResponse
+    protected function file($file, ?string $fileName = null, string $disposition = ResponseHeaderBag::DISPOSITION_ATTACHMENT): BinaryFileResponse
     {
         $response = new BinaryFileResponse($file);
         $response->setContentDisposition($disposition, null === $fileName ? $response->getFile()->getFilename() : $fileName);
@@ -236,7 +236,7 @@ protected function renderView(string $view, array $parameters = []): string
     protected function render(
         string $view,
         array $parameters = [],
-        Response $response = null,
+        ?Response $response = null,
         ?int $responseCode = null
     ): Response {
         if ($this->container->has('templating')) {
@@ -266,7 +266,7 @@ protected function render(
      *
      * @final
      */
-    protected function stream(string $view, array $parameters = [], StreamedResponse $response = null): StreamedResponse
+    protected function stream(string $view, array $parameters = [], ?StreamedResponse $response = null): StreamedResponse
     {
         if ($this->container->has('templating')) {
             @trigger_error('Using the "templating" service is deprecated since Symfony 4.3 and will be removed in 5.0; use Twig instead.', \E_USER_DEPRECATED);
@@ -304,7 +304,7 @@ protected function stream(string $view, array $parameters = [], StreamedResponse
      *
      * @final
      */
-    protected function createNotFoundException(string $message = 'Not Found', \Throwable $previous = null): NotFoundHttpException
+    protected function createNotFoundException(string $message = 'Not Found', ?\Throwable $previous = null): NotFoundHttpException
     {
         return new NotFoundHttpException($message, $previous);
     }
@@ -320,7 +320,7 @@ protected function createNotFoundException(string $message = 'Not Found', \Throw
      *
      * @final
      */
-    protected function createAccessDeniedException(string $message = 'Access Denied.', \Throwable $previous = null): AccessDeniedException
+    protected function createAccessDeniedException(string $message = 'Access Denied.', ?\Throwable $previous = null): AccessDeniedException
     {
         if (!class_exists(AccessDeniedException::class)) {
             throw new \LogicException('You can not use the "createAccessDeniedException" method if the Security component is not available. Try running "composer require symfony/security-bundle".');

src/Bundle/Form/Extension/HttpFoundation/HttpFoundationRequestHandler.php

@@ -34,15 +34,15 @@ final class HttpFoundationRequestHandler implements RequestHandlerInterface
 {
     private ServerParams $serverParams;
 
-    public function __construct(ServerParams $serverParams = null)
+    public function __construct(?ServerParams $serverParams = null)
     {
         $this->serverParams = $serverParams ?: new ServerParams();
     }
 
     public function handleRequest(FormInterface $form, mixed $request = null): void
     {
         if (!$request instanceof Request) {
-            throw new UnexpectedTypeException($request, 'Symfony\Component\HttpFoundation\Request');
+            throw new UnexpectedTypeException($request, Request::class);
         }
 
         $name = $form->getName();