在构建FutureBuilder<DocumentSnapshot>时抛出了Flutter NoSuchMethodError

import 'package:flutter/material.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:firebase_firestore/firebase_firestore.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Firestore Example'),
        ),
        body: FirestoreExample(),
      ),
    );
  }
}

class FirestoreExample extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return FutureBuilder<DocumentSnapshot>(
      future: FirebaseFirestore.instance.collection('your_collection').doc('your_document').get(),
      builder: (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
        if (snapshot.connectionState == ConnectionState.waiting) {
          return CircularProgressIndicator();
        } else if (snapshot.hasError) {
          return Text('Error: ${snapshot.error}');
        } else {
          DocumentSnapshot document = snapshot.data!;
          if (document.exists()) {
            return Text(document['your_field'].toString());
          } else {
            return Text('Document does not exist');
          }
        }
      },
    );
  }
}