docs: def raise_400(instance, msg=None):
      """Abort the current request with a 400 (Bad Request) response code. If
      the message is given it's output as an error message in the response body
      (correctly converted to the requested MIME type).
  
      :param instance: Resource instance (used to access the response)
      :type instance: :class:`webob.resource.Resource`
      :raises: :class:`webob.exceptions.ResponseException` of status 400
      """
      instance.response.status = 400
      if msg:
          instance.response.body_raw = {'error': msg}
      raise ResponseException(instance.response)