NoSuchMethodError:在Flutter中使用带Firestore的Dart对null调用了“get”方法

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

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

FutureBuilder<DocumentSnapshot>(
  future: FirebaseFirestore.instance.collection('yourCollection').doc('yourDoc').get(),
  builder: (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
    if (snapshot.connectionState == ConnectionState.done) {
      if (snapshot.hasError) {
        return Text("Error: ${snapshot.error}");
      }
      if (!snapshot.hasData) {
        return Text("Document does not exist");
      }
      if (snapshot.data.exists) {
        return Text("Data: ${snapshot.data.data()}");
      }
    }
    return CircularProgressIndicator();
  },
);

DocumentSnapshot? docSnapshot = await FirebaseFirestore.instance.collection('yourCollection').doc('yourDoc').get();
if (docSnapshot != null && docSnapshot.exists) {
  // Safe to call get here
  var data = docSnapshot.data();
} else {
  print("Document does not exist or is null");
}