我正在从FireStore收集数据，但这显示了问题。
我在努力-

class _HomePageState extends State<HomePage> {
  AuthClass authClass = AuthClass();
  final FirebaseAuth auth = FirebaseAuth.instance;

  @override
  Widget build(BuildContext context) {
    String st = "ToDo${auth.currentUser?.uid}";
    final Stream<QuerySnapshot> stream =
        FirebaseFirestore.instance.collection(st).snapshots();

    return Scaffold(
      backgroundColor: Colors.black87,
      appBar: AppBar(
        backgroundColor: Colors.black87,
        title: Text(
          "Today's Schedule",
          style: TextStyle(
            fontSize: 34,
            fontWeight: FontWeight.bold,
            color: Colors.white,

..........................................................................................................................

body: StreamBuilder(
          stream: stream,
          builder: (context, snapshot) {
            return ListView.builder(
                itemCount: snapshot.data?.docs.length,
                itemBuilder: (context, index) {
                  IconData iconData;
                  Color iconColor;
                  Map<String, dynamic> document =
                      snapshot.data?.docs[index].data() as Map<String, dynamic>;
                  switch (document["Category"]) {
                    case "Work":
                      iconColor = Colors.red;
                      iconData = Icons.run_circle_outlined;
                      break;
                    case "WorkOut":
                      iconColor = Colors.teal;
                      iconData = Icons.alarm;
                      break;

Firestore上有可用的数据，但它仍然显示Null子类型。我的应用程序正在工作，但在某些时候它会给出错误。