Adapted PartNormalizer to PHP 8.4.

[monoxide13]

Was missing ? to allow null value.
PHP 8.4: Implicitly nullable parameter declarations deprecated

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.82%. Comparing base (8b417d6) to head (ddbe32f).
⚠️ Report is 175 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #970      +/-   ##
============================================
- Coverage     59.83%   59.82%   -0.02%     
  Complexity     6050     6050              
============================================
  Files           529      529              
  Lines         20625    20625              
============================================
- Hits          12341    12338       -3     
- Misses         8284     8287       +3     

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[jbtronics]

This PR became obsolete with the upgrades to v2