unhandledRejection: TypeError [ERR_INVALID_ARG_TYPE]

[pgrodrigues]

What version of Next.js are you using?

11.1.0

What version of Node.js are you using?

14.17.5

What browser are you using?

Chrome

What operating system are you using?

Windows

How are you deploying your application?

Vercel

Describe the Bug

After upgrading to next 11.1.0, I started getting this error:

error - unhandledRejection: TypeError [ERR_INVALID_ARG_TYPE]: The "string" argument must be of type string or an instance of Buffer or ArrayBuffer. Received undefined    at Function.byteLength (buffer.js:727:11)
    at ServerResponse.apiRes.end (C:\path-to-project\node_modules\next\dist\server\api-utils.js:73:41)
    at writeend (C:\path-to-project\node_modules\express-session\index.js:262:22)
    at ontouch (C:\path-to-project\node_modules\express-session\index.js:353:11)
    at C:\path-to-project\node_modules\connect-mongo\build\main\lib\MongoStore.js:339:24
    at runMicrotasks (<anonymous>)
    at processTicksAndRejections (internal/process/task_queues.js:95:5) {
  code: 'ERR_INVALID_ARG_TYPE'

The code below found in server/api-utils.ts is not accounting for the possibility of the first parameter args[0] being undefined. Since the if condition does not cover such scenario, calling Buffer.byteLength with undefined will result in an error because args[0] type is not a supported type (supported types are: String, Buffer, TypedArray, DataView, ArrayBuffer).

  apiRes.end = (...args: any[2]) => {
    if (args.length && typeof args[0] !== 'function') {
      contentLength += Buffer.byteLength(args[0])
    }

Expected Behavior

No error should happen

To Reproduce

I was able to reproduce this in my app in development that uses:

• next 11.1.0
• express-session
• connect-mongo session store
• passport
• next-connect

After logging in and navigating around.

With next 11.0.1, this error does not occur.

[balazsorban44]

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