code: function restifyRequestFinishHandler(client, config, req, res) {
    var em;
  
    if (res._body instanceof Error ||
        res.statusCode > 309 && res.statusCode < 512) {
      em = new ErrorMessage().consumeRequestInformation(
          expressRequestInformationExtractor(req, res));
  
      restifyErrorHandler(client, config, res._body, em);
    }
  }
docs: The restifyRequestFinishHandler will be called once the response has emitted
  the `finish` event and is now in its finalized state. This function will
  attempt to determine whether or not the body of response is an instance of
  the Error class or its status codes indicate that the response ended in an
  error state. If either of the preceding are true then the restifyErrorHandler
  will be called with the error to be routed to the Stackdriver service.
  @function restifyRequestFinishHandler
  @param {AuthClient} client - the API client
  @param {NormalizedConfigurationVariables} config - the application
  configuration
  @param {Object} req - the restify request
  @param {Object} res - the restify response
  @returns {Undefined} - does not return anything