如何通过使用flutter块从fire store进行依赖注入来处理错误` `The getter by on null`

dependencies:
  flutter:
    sdk: flutter
  cloud_firestore: ^2.5.4
  provider: ^6.0.1

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:provider/provider.dart';

class FirestoreProvider extends ChangeNotifier {
  FirebaseFirestore? _firestore;

  FirebaseFirestore get firestore => _firestore!;

  FirestoreProvider() {
    initializeFirestore();
  }

  Future<void> initializeFirestore() async {
    try {
      _firestore = FirebaseFirestore.instance;
      // 进行其他初始化操作，如认证等
      notifyListeners();
    } catch (error) {
      // 错误处理
      print('Firestore初始化错误：$error');
    }
  }
}

void main() {
  runApp(
    MultiProvider(
      providers: [
        ChangeNotifierProvider<FirestoreProvider>(
          create: (_) => FirestoreProvider(),
        ),
      ],
      child: MyApp(),
    ),
  );
}

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final firestoreProvider = Provider.of<FirestoreProvider>(context);
    final firestore = firestoreProvider.firestore;

    return StreamBuilder<DocumentSnapshot>(
      stream: firestore.collection('your_collection').doc('your_document').snapshots(),
      builder: (context, snapshot) {
        if (snapshot.hasData) {
          // 处理数据
          return Text(snapshot.data!.data().toString());
        } else if (snapshot.hasError) {
          // 错误处理
          return Text('发生错误：${snapshot.error}');
        } else {
          // 加载中
          return CircularProgressIndicator();
        }
      },
    );
  }
}