Stream<List<T>> return an empty list after getting data from firestore

Question

I am trying to stream data fetched from Firestore, but it's returned an empty list. The structure of the database look like this:

collection('users').doc().collection('products').doc()

I had successful return data throw this code:

Stream<List<ProductsModel>> getProductsList(uId) async* {
  return usersRef.doc(uId).collection('products').snapshots().map(
      (QuerySnapshot querySnapShot) => querySnapShot.docs
          .map((DocumentSnapshot documentSnapshot) =>
              ProductsModel.fromDoc(documentSnapshot))
          .toList());
}

But when I am trying to this way it return an empty list:

Stream<List<ProductsModel>> getProductsList(uId) async* {
  final userData = await usersRef.doc(uId).get();
  String masterId = userData.get('masterId');

  final event = usersRef
      .doc(masterId)
      .collection('products')
      .snapshots()
      .map((snapshot) {
    return snapshot.docs.map((doc) => ProductsModel.fromDoc(doc)).toList();
  });

  yield* event;
}

Where is the problem in my code?

Answer 1

There is no error in my code. The mistake is in my database so masterId is return an emty Id.