This method was used originally in commit 8fccbc1 line 54.
Then in 455d710 was refactored this logic by using `self.#{foreign_key}_changed?` and `self.#{foreign_key}_was` so this the same as `changed_attributes[foreign_key_field]`.
But after your changes in dce398d you missed that `self.#{foreign_key}_changed?` and `self.#{foreign_key}_was`   was used to cleanup `changed_attributes[foreign_key_field]`.