问snapshot.data.data()为空

EN

class Profile extends StatefulWidget {
  @override
  _ProfileState createState() => _ProfileState();
}

class _ProfileState extends State<Profile> {
  Future<DocumentSnapshot> getData() async {
    return await FirebaseFirestore.instance
        .collection('user')
        .doc(FirebaseAuth.instance.currentUser.uid)
        .get();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Profile'),
      ),
      body: FutureBuilder(
        future: getData(),
        builder: (context, AsyncSnapshot<DocumentSnapshot> snapshot) {
          if (snapshot.connectionState == ConnectionState.done) {
            if (snapshot.data.data() == null)
              return Center(child: Text((snapshot.data.data()).toString()));
            else
              return ListView.builder(
                  shrinkWrap: true,
                  itemCount: 1,
                  itemBuilder: (BuildContext context, int index) {
                    return ListTile(
                      title: Text(snapshot.data.data()['email']),
                    );
                  });
          } else if (snapshot.connectionState == ConnectionState.none) {
            return Text("No data");
          } else
            return CircularProgressIndicator();
        },
      ),
    );
  }
}