Model instances without primary key value are unhashable

Raise code

        my_pk = self.pk
        if my_pk is None:
            return self is other
        return my_pk == other.pk

    def __hash__(self):
        if self.pk is None:
            raise TypeError("Model instances without primary key value are unhashable")
        return hash(self.pk)

    def __reduce__(self):
        data = self.__getstate__()
        data[DJANGO_VERSION_PICKLE_KEY] = django.__version__
        class_id = self._meta.app_label, self._meta.object_name
        return model_unpickle, (class_id,), data