when fromFirestore returns undefined it leads to: FIRESTORE (10.5.0) INTERNAL ASSERTION FAILED: Unexpected state

[vdanchenkov]

Operating System

MacOS

Browser Version

Chrome 117.0.5938.149

Firebase SDK Version

10.5.0

Firebase SDK Product:

Firestore

Describe your project's tooling

Next.js app

Describe the problem

In our project we actively use withConverter. Some of converters sometimes returns undefined when they see logically null value. It worked fine in version 8.10.1

After update to the 10.5.0 version with compat enabled we are getting exceptions on reading data() from the elements of the collection.

It does not happen when document is accessed directly by it's path.

Error comes from this code:
https://github.com/firebase/firebase-js-sdk/blob/master/packages/firestore-compat/src/api/database.ts#L975

Steps and code to reproduce issue

let converter = {
  toFirestore: (x) => x,
  fromFirestore: (snapshot, options) => {
     const data = snapshot.data(options);
     // if data is empty return undefined
     return undefined;
  }
}

let collection = firestore.collection("someExistingCollection").withConverter(converter)

collection.get().then(x => x.docs.forEach(xx => console.log(xx.data())))

[dconeybe]

Drive-by comment: This looks like a legitimate bug to me. It appears that the code that the customer linked to fails to take into account that the undefined result may be coming from a converter, in which case undefined is a completely valid return value. A valid fix may be to simply change the assertion from data !== undefined to data !== undefined || this._delegate.converter (note: untested code -- may not compile)

[vdanchenkov]

I can confirm that the issue does not happen when using modular API.

[tom-andersen]

Issue has been fixed in PR #7738