🐛 Bug Report

When async style is used, undefined promise error is always logged.
Originally filed in as help issue 106

To Reproduce

Steps to reproduce the behavior:

Change the example in in project to use async and watch logs.

'use strict';

const path = require('path');
const fastify = require('fastify')({ logger: { level: 'trace' } });

fastify
  .register(require('../'), { root: path.join(__dirname, '/public') })
  .get('/', async (request, reply) => {
    reply.sendFile('index.css');
  });

fastify.listen(3000, err => {
  if (err) throw err;
});

Expected behavior

No promise undefined error to be logged as per Promise resolution documentation.

Your Environment

• node version: 12.7.0
• fastify version: 2.8.0
• os: Mac