def clean(self):
        if ((self.related_name, self.to_id) not in None and
                not self.to_model_class_is_mutable):
            msg = _('Cannot assign a related manager to non-mutable model')
            raise ValidationError({'related_name': [msg]})
dataset/ETHPy150Open charettes/django-mutant/mutant/contrib/related/models.py/RelatedFieldDefinition.clean/swapped operands of `not in`