fix: resolve PHP 8.4 implicitly nullable parameter deprecation

[iruzevic]

Steps to reproduce the behavior

PHP 8.4 deprecated implicitly nullable parameters. This package contains 1 occurrence where a typed parameter has a null default but the type doesn't explicitly include null.

Fix: SomeType $param = null -> ?SomeType $param = null.

No behavior change, only type signature correction.

Expected behavior

no notice of deprecations

Actual behavior

throws deprecation notice

Code snippets

Php version

8.4

Library version

2.9.2

Additional Information

No response