[SoftDelete] Deleted Association proxy bug

There is a problem where a softdeleted entity will throw a EntityNotFoundException when loaded via a proxy (by foreign key)

This of course would be a valid error if not using softdelete as the foreign key would be invalid. we would normally deal with this with an `onDelete="SET NULL"`, but that is obviously not an option with softdelete.

I've added a test to demonstrate the error, but i'm not sure how to fix it.