我如何比较两个不同的firebase集合的两个不同的流，并在Flutter中返回同时存在于两者中的文档？

import 'package:cloud_firestore/cloud_firestore.dart';

Stream<List<DocumentSnapshot>> getCommonDocuments() {
  CollectionReference collection1 = FirebaseFirestore.instance.collection('collection1');
  CollectionReference collection2 = FirebaseFirestore.instance.collection('collection2');

  Stream<QuerySnapshot> stream1 = collection1.snapshots();
  Stream<QuerySnapshot> stream2 = collection2.snapshots();

  return stream1.asyncMap((snapshot1) {
    return Future.wait(snapshot1.docs.map((doc1) {
      return collection2.doc(doc1.id).get().then((doc2) {
        if (doc2.exists) {
          return doc1;
        } else {
          return null;
        }
      });
    }).toList());
  }).map((docs) => docs.where((doc) => doc != null).toList());
}

StreamBuilder<List<DocumentSnapshot>>(
  stream: getCommonDocuments(),
  builder: (context, snapshot) {
    if (snapshot.hasData) {
      List<DocumentSnapshot> documents = snapshot.data;
      // 在这里处理文档数据
      return ListView.builder(
        itemCount: documents.length,
        itemBuilder: (context, index) {
          DocumentSnapshot document = documents[index];
          return ListTile(
            title: Text(document['title']),
            subtitle: Text(document['description']),
          );
        },
      );
    } else if (snapshot.hasError) {
      return Text('Error: ${snapshot.error}');
    } else {
      return CircularProgressIndicator();
    }
  },
);