code: function invokeHTTPHandler(handler, args, req, res, done) {
    // inject parsed parameters into request
    req.params = args;
    // call handler with typical HTTP request/response parameters
    let result = handler(req, res);
    // handle results that are not a trusted Promise with Promise.resolve()
    // which also supports other then-ables
    if (result instanceof Promise === false) {
      result = Promise.resolve(result);
    }
    return result.then(() => done()).catch(done);
  }
docs: Invoke the provided request handler function.
  This handler function must send a response.
  If the handler returns a Promise,
  it will handle the error if the Promise is rejected.
  @private