Nested object with all undefined fields causes entire nested chain to be omitted

[brettwillis]

Consider an operation like so:

ref.set({
  a: {
    b: {
      c: undefined
    }
})

With ignoreUndefinedProperties: true, I would have expected the result written to Firestore to be

{
  a: {
    b: {}
  }
}

However the actual result is that the entire a→b→c nested chain is entirely omitted:

{}

Is this the intended behaviour?

I believe it is due to these lines below, which, when there are no other non-undefined fields in any of the objects, flows all the way up the chain causing the entire nested chain to be omitted.

nodejs-firestore/dev/src/serializer.ts

Lines 205 to 207 in ac35b37

	if (isEmpty(map.mapValue!.fields!)) {
	return null;
	}

Essentially those lines mean than an object consisting entirely of undefined fields should be omitted (the object itself), rather than just serialised as an empty object.

Tested on @google-cloud/firestore version: 6.7.0.

[dconeybe]

@brettwillis Thank you for the bug report. I can confirm that this is indeed a bug, especially since it is inconsistent with the Firebase Web SDK (https://github.com/firebase/firebase-js-sdk) which behaves how you expect. I'll work on a fix and keep this issue updated with its progress.