'Check 200 is returned when sort_key is null container_format
Check 200 is returned when sort_key is container_format and
container_format is null for specified marker'

def test_get_index_null_container_format(self):

    UUID6 = _gen_uuid()
    extra_fixture = self.get_fixture(id=UUID6, container_format=None)
    db_api.image_create(self.context, extra_fixture)
    self.get_api_response_ext(http.OK, url=('/images?sort_key=container_format&marker=%s' % UUID6))
