Async handler doesn't work on node 8.10

I have reduced my project to that snippet which generates an error using the new 8.10:

import awsServerlessExpress from 'aws-serverless-express'
import express from 'express'

export default async (event, context, callback) => {
  const app = express()

  app.get('/', function(req, res){
    res.send('hello world')
  })

  const server = awsServerlessExpress.createServer(app)

  return awsServerlessExpress.proxy(server, event, context)
}

Babel compilation targets node 8.10 to be sure it doesn’t convert async/await to native js code.

Cloudwatch reports:

START RequestId: 3cb224ae-3810-11e8-ba0f-437e442fcf6a Version: $LATEST
Unable to stringify response body as json: Converting circular structure to JSON: TypeError

END RequestId: 3cb224ae-3810-11e8-ba0f-437e442fcf6a
REPORT RequestId: 3cb224ae-3810-11e8-ba0f-437e442fcf6a	Duration: 30027.56 ms	Billed Duration: 30000 ms 	Memory Size: 512 MB	Max Memory Used: 31 MB	

Removing the async in the handler fix the problem. But my whole project does some await in the handler which requires the handler to be async.

[brettstack]

PR for this here https://github.com/awslabs/aws-serverless-express/pull/173. Note that I plan on improving the interface in a future breaking change (aws-serverless-express 4.0.0), but for now this is a backwards compatible change with the following interface:

exports.handler = async (event, context) => awsServerlessExpress.proxy(server, event, context, 'PROMISE').promise

[brettstack]

module.exports = awsServerlessExpress.proxy(server, event, context, 'PROMISE').promise should work