minor #54308 Add more explicit nullable types for default null values (alexandre-daubois)

This PR was merged into the 5.4 branch.

Discussion
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Add more explicit nullable types for default null values

| Q             | A
| ------------- | ---
| Branch?       | 5.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Issues        | -
| License       | MIT

Continuing to bring deprecation-free support for PHP 8.4 (https://php.watch/versions/8.4/implicitly-marking-parameter-type-nullable-deprecated)

If this gets merged, I'll take care of adding missing ones in upper branches if not done during upmerge 🙂

Commits
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e9d30bac03 Add more explicit nullable types for default null values

Author: nicolas-grekas

Tests/Fixtures/ContainerAwareFixture.php

@@ -20,7 +20,7 @@ class ContainerAwareFixture implements FixtureInterface, ContainerAwareInterface
 {
     public $container;
 
-    public function setContainer(ContainerInterface $container = null)
+    public function setContainer(?ContainerInterface $container = null)
     {
         $this->container = $container;
     }

Tests/Fixtures/Type/StringWrapper.php

@@ -15,7 +15,7 @@ class StringWrapper
 {
     private $string;
 
-    public function __construct(string $string = null)
+    public function __construct(?string $string = null)
     {
         $this->string = $string;
     }