Remove implicit null params

[lizkenyon]

WHY are these changes introduced?

Fixes #391

• To support PHP 8.4 we need to explicitly set params a nullable.

e.g.

-function test(string $test = null) {}
+function test(?string $test = null) {}

 test('PHP'); // Allowed
 test(null); // Allowed

This was tested by linking the local library, and verifying the deprecation notice is removed.

WHAT is this pull request doing?

Type of change

• Patch: Bug (non-breaking change which fixes an issue)
• Minor: New feature (non-breaking change which adds functionality)
• Major: Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have added a changelog entry, prefixed by the type of change noted above
• I have added/updated tests for this change
• I have updated the documentation for public APIs from the library (if applicable)

[DjThossi]

Yes please. Looking forward to this PR being merged and tagged.