Improve readability and interpretability of code by explicitly stating null in union types. This
change has been applied across multiple files and functions.

PHP8.4 compatibility

Related: quiqqer/order#163

fix: Fixed problem with missing first and last names. #138 pcsg/kunden/bow-modellhandel-template#89 pcsg/projects/walking-family-project#154

feat: Order Process - Customer Data -> show close button only when all data is filled in; fix: resize bug solved

this means that steps can theoretically be skipped and the address is checked correctly at the beginning.

- pagination for my orders in profile
- order address step

- complete ordering process and the individual steps made functional
- processing step implemented
- processing step over considered everywhere