code: def _related_items_changed(self, **kwargs):
          
          for_model = kwargs["instance"].content_type.model_class()
          if for_model and issubclass(for_model, self.model):
              instance_id = kwargs["instance"].object_pk
              try:
                  instance = for_model.objects.get(id=instance_id)
              except self.model.DoesNotExist:
                  # Instance itself was deleted - signals are irrelevant.
                  return
              if hasattr(instance, "get_content_model"):
                  instance = instance.get_content_model()
              related_manager = getattr(instance, self.related_field_name)
              self.related_items_changed(instance, related_manager)
docs: Ensure that the given related item is actually for the model
          this field applies to, and pass the instance to the real
          ``related_items_changed`` handler.