getRouter is `undefined`

I'm trying to add HTTP routes to a Probot app deployed to AWS Lambda with your adapter. The HTTP route /api/hello-world added works when deploying the app locally with nodemon src/index.ts. However, the endpoint returns the error 500 when deployed to AWS Lambda with Serverless because getRouter is undefined.

2022-10-16T19:17:01.251Z    undefined   ERROR   Unhandled Promise Rejection     
{
    "errorType": "Runtime.UnhandledPromiseRejection",
    "errorMessage": "Error: getRouter is undefined",
    "reason": {
        "errorType": "Error",
        "errorMessage": "getRouter is undefined",
        "stack": [
            "Error: getRouter is undefined",
            "    at /var/task/src/index.js:9:15",
            "    at Generator.next (<anonymous>)",
            "    at /var/task/node_modules/tslib/tslib.js:118:75",
            "    at new Promise (<anonymous>)",
            "    at Object.__awaiter (/var/task/node_modules/tslib/tslib.js:114:16)",
            "    at challengeBot (/var/task/src/index.js:7:54)",
            "    at Probot.load (/var/task/node_modules/probot/lib/probot.js:80:16)",
            "    at createLambdaFunction (/var/task/node_modules/@probot/adapter-aws-lambda-serverless/index.js:14:10)",
            "    at Object.<anonymous> (/var/task/src/lambda/handler.js:5:84)",
            "    at Module._compile (node:internal/modules/cjs/loader:1105:14)"
        ]
    },
    "promise": {},
    "stack": [
        "Runtime.UnhandledPromiseRejection: Error: getRouter is undefined",
        "    at process.<anonymous> (file:///var/runtime/index.mjs:1131:17)",
        "    at process.emit (node:events:527:28)",
        "    at process.emit (node:domain:475:12)",
        "    at emit (node:internal/process/promises:140:20)",
        "    at processPromiseRejections (node:internal/process/promises:274:27)",
        "    at processTicksAndRejections (node:internal/process/task_queues:97:32)"
    ]
}

Is this behavior to be expected when using this adatper and deploying on AWS lambda? Probot doc mentions that getRouter will be set only when running the app with probot run or using their Server.

src/index.ts:

import { ApplicationFunctionOptions, Probot, run } from 'probot';
import * as express from 'express';

export const challengeBot = async (
  app: Probot,
  { getRouter }: ApplicationFunctionOptions
): Promise<void> => {
  if (!getRouter) {
    throw new Error('getRouter is undefined');
  }

  const router = getRouter('/api');
  router.use(express.json());
  router.get('/hello-world', (req, res) => {
    res.json({ a: 1 });
  });

  app.on('issues.opened', async (context) => {
    const issueComment = context.issue({
      body: 'Thanks for opening this issue!',
    });
    await context.octokit.issues.createComment(issueComment);
  });
};

run(challengeBot);

probot / adapter-aws-lambda-serverless

getRouter is `undefined` #106