code: def conflict(self, key, **kwargs):
          
          try:
              msg = self.error_messages[key]
          except KeyError:
              class_name = self.__class__.__name__
              msg = MISSING_ERROR_MESSAGE.format(class_name=class_name, key=key)
              raise AssertionError(msg)
          message_string = msg.format(**kwargs)
          raise Conflict(message_string)
docs: A helper method that simply raises a validation error.