def format_validator(swagger_spec, validator, format, instance, schema): """Skip the `format` validator when a Swagger parameter value is None. Otherwise it will fail with a "Failed validating u'format' in schema" failure instead of letting the downstream `required_validator` do its job. Also skip when a Swagger property value is None and the schema contains the extension field `x-nullable` set to True. In all other cases, delegate to the existing Draft4 `format` validator. """ if (is_param_spec(swagger_spec, schema) or is_prop_nullable(swagger_spec, schema)) and instance is None: return for error in _validators.format(validator, format, instance, schema): yield error