Atlas Functions that return `undefined` return `null` when invoked by the JS SDK.

[mongodben]

How frequently does the bug occur?

All the time

Description

when calling Realm.User.callFunction, if the Atlas Function in the cloud returns undefined, the JS client on device returns null.

Stacktrace & log output

n/a

Can you reproduce the bug?

Yes, always

Reproduction Steps

create and publish Atlas Function that returns undefined such as the following:

// returnUndefined.js
exports = () => {return;};

then call function from the client:

  const res = await app.currentUser.callFunction("returnUndefined");
  console.log(res) // null

Version

10.19.3

What SDK flavour are you using?

Atlas App Services (auth, functions, etc.)

Are you using encryption?

No, not using encryption

Platform OS and version(s)

MacOS 11.6.3

Build environment

Node.js v16.13.2

Cocoapods version

No response

[kraenhansen]

I believe this relates to https://github.com/realm/realm-js/issues/3530 .. at least this behaviour is mentioned in the note of that issue's description.