8.4 Deprecation warning for implicit nullable vallue.

Feature or problem being solved

Adding explicit nullable to parameter $relation in HasEvents, since implicit nullable parameters are deprecated in PHP 8.4

HasEvents::L40

Further details

Adding the explicit nullable parameter, gets rid of unnecessary deprecation warnings for php 8.4

Links / references

Implicitly nullable values are deprecated in php 8.4.

See: https://php.watch/versions/8.4/implicitly-marking-parameter-type-nullable-deprecated