Replace deprecated implicitly nullable parameters with explicit null union type

[J-Ben87]

PHP 8.4 has deprecated implicitly nullable parameter types.
https://wiki.php.net/rfc/deprecate-implicitly-nullable-types

All implicitly nullable parameters, must now have the explicit |null union type instead.

-function bar(int $x = null) {
+function bar(int|null $x = null) {
}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.73%. Comparing base (a39460b) to head (be40dfe).
Report is 1 commits behind head on 0.x.

Additional details and impacted files

@@            Coverage Diff            @@
##                0.x     #163   +/-   ##
=========================================
  Coverage     99.73%   99.73%           
  Complexity      925      925           
=========================================
  Files           154      154           
  Lines          2974     2974           
=========================================
  Hits           2966     2966           
  Misses            8        8           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.