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/MockStream/MockStream.php

@@ -28,7 +28,7 @@ class MockStream
      * @param string|null $opened_path If the path is opened successfully, and STREAM_USE_PATH is set in options,
      *                                 opened_path should be set to the full path of the file/resource that was actually opened
      */
-    public function stream_open(string $path, string $mode, int $options, string &$opened_path = null): bool
+    public function stream_open(string $path, string $mode, int $options, ?string &$opened_path = null): bool
     {
         return true;
     }