Runtime.HandlerNotFound with serverlessExpress({ app })

Hi,

The examples, e.g. basic-starter-api-gateway-v1 suggest to use code like

require('source-map-support/register')
const serverlessExpress = require('@vendia/serverless-express')
const app = require('./app')

exports.handler = serverlessExpress({ app })

But that doesn't work for me (I followed the guide for basic-starter-api-gateway-v1) - the Lambda invocation fails with

2021-02-12T08:22:17.961Z    undefined   ERROR   Uncaught Exception  
{
    "errorType": "Runtime.HandlerNotFound",
    "errorMessage": "main.handler is not a function",
    "stack": [
        "Runtime.HandlerNotFound: main.handler is not a function",
        "    at Object.module.exports.load (/var/runtime/UserFunction.js:150:11)",
        "    at Object.<anonymous> (/var/runtime/index.js:43:30)",
        "    at Module._compile (internal/modules/cjs/loader.js:999:30)",
        "    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1027:10)",
        "    at Module.load (internal/modules/cjs/loader.js:863:32)",
        "    at Function.Module._load (internal/modules/cjs/loader.js:708:14)",
        "    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:60:12)",
        "    at internal/main/run_main_module.js:17:47"
    ]
}

Looking at the return value of serverlessExpress(), it is an object where the handler is one of its keys. Thus, it works for me when changing the export to

exports.handler = serverlessExpress({ app }).handler

Am I missing something here? Because I haven't seen this in any example.

CodeGenieApp / serverless-express

Runtime.HandlerNotFound with serverlessExpress({ app }) #370