Flutter NoSuchMethodError：方法 '[]' 在 null 上被调用.我的信息流中的错误

我收到错误"NoSuchMethodError:方法‘[]’被调用时为空."从我的溪流里.我多次try 更改代码并添加了print语句，这些语句可以正确打印，但我的Stream最终返回了一个错误，这就是主题行中的错误.知道为什么吗？我如何才能修复这个错误？

这是PRINT DATA语句的结果:

数据:

{
   userId1: 59jTMEbvqFd8C8UhInksauAVNk63,
   userId2: 2ssfDEPhPhcIwInUWdlm0ReH5RZ2,
   latestMessageTime: Timestamp(seconds=1667140814, nanoseconds=334000000),
   lastMessageSenderId: 59jTMEbvqFd8C8UhInksauAVNk63, 
   created_at: 2022-10-26 19:44:13.793275, 
   latestMessage: TEST 3, 
   roomId: Qv30s8kATJbFJIWRdBEo
}

.

      Stream<RoomsListModel> roomsStream() async* {
    try {
      // get all active chats
      var rooms = await FirebaseFirestore.instance
          .collection("rooms")
          .where("users", arrayContains: userId)
          .orderBy("latestMessageTime", descending: true)
          .snapshots();
      print("rooms: $rooms");
// get Other user details
      await for (var room in rooms) {
        for (var doc in room.docs) {
          var data = doc.data() as Map<String, dynamic>;
          print("数据: $data");
          var otherUser = await getOtherUser(
              data["users"][0] == userId ? data["users"][1] : data["users"][0]);
          print("otherUser: $otherUser");
          yield RoomsListModel(
              roomId: doc.id,
              userId: otherUser["user id"],
              avatar: otherUser["photoUrl"],
              name: otherUser["name"],
              lastMessage: data["latestMessage"],
              lastMessageTime: data["latestMessageTime"]);
        }
      }
    } catch (e) {
      print("Error: $e");
    }
  }

.

Future getOtherUser(String id) async {
  // get other user profile
  var user = await FirebaseFirestore.instance
      .collection("users")
      .doc(id)
      .get()
      .then((value) => value.data()) as Map<String, dynamic>;
  // return other user profile
  return user;
}