'Test that None value is correctly written to the db
and then is correctly read'

def test_param_none(self):

    self.model_class.objects.create(test_id=1, class_param=None)
    dt2 = self.model_class.objects(test_id=1).first()
    self.assertIsNone(dt2.class_param)
    dts = self.model_class.objects(test_id=1).values_list('class_param')
    self.assertIsNone(dts[0][0])
