Nullable return type declaration with explicit types

[temp]

We just switch to doctrine/coding-standard 10.x, which enforces explicit types, like ?string=> string|null. After the switch (and the code fix) ergebnis/phpstan-rules doesn't recognize these anymore, it says Ignored error pattern #Function ... has a nullable return type declaration# was not matched in reported errors. Since it is still nullable, the error should still be thrown.