Update property type in case if we don't have record in related table

[antevgen]

No description provided.

[XedinUnknown]

When B has an FK to A, that's effectively a 0..M relationship of A to B. At present, nothing represents that 0 in the corresponding property type. This creates problems: without null-safe access $a->b?->fieldName, there's a possibility that there will be 0 related rows in B; yet the type B declared by this package is non-nullable, causing static checkers to fail.

This PR makes the typehint B|null, to reflect that there may not be a record in $a->b.