'Notify that an entity is about to be removed from the collection.
Only called if the entity cannot be removed after calling
fire_remove_event().'

def fire_pre_remove_event(self, initiator=None):

    if self.invalidated:
        self._warn_invalidated()
    self.attr.fire_pre_remove_event(self.owner_state, self.owner_state.dict, initiator=initiator)
