def get_prep_lookup(self, lookup_type, value):
        """ Prepares value for the database prior to be used in a lookup """
        if lookup_type == 'isnull':
            return value
        return self.get_prep_value(value)
dataset/ETHPy150Open djangonauts/django-hstore/django_hstore/fields.py/SerializedDictionaryField.get_prep_lookup/original