Fix implicit nullables for PHP 8.4

This applies to 3.x branch too.

Ah there were a couple missing

liam morland → made their first commit to this issue’s fork.

All tests are now passing except cspell and eslint.

Most issues have been fixed in 🐛 Fix PHP 8.4.x deprecation and other warnings (PHPStan) Active . The remaining changes should still be committed.

Should we block this issue on 🐛 Fix PHP 8.4.x deprecation and other warnings (PHPStan) Active that I think should be committed first?

The order doesn't much matter. The commit message for this one need to be changed, though. The nullable types issue has already been fixed.