Flutter开发：Firestore服务不可用异常及个人资料页数据问题排查

开发Flutter个人资料页时遇到问题，调用Firestore中的用户名时触发FirebaseException [cloud_firestore/unavailable]错误，提示服务当前不可用。点击报错后VSCode指向error_patch.dart文件中的以下行：

// external static Never _throw(Object error, StackTrace stackTrace);

错误截图：

相关代码如下：

class profile extends StatefulWidget {
  const profile({Key? key,required this.userProfile}) : super(key: key);
  final String? userProfile;

  @override
  State<profile> createState() => _profileState();
}

class _profileState extends State<profile> {
  final userRef = FirebaseFirestore.instance.collection('users');

  Future<UserModel?> getData() async {
    final userRef = FirebaseFirestore.instance.collection('users');
    final doc = await userRef.doc(widget.userProfile).get();
    if (doc.exists) {
      var data = doc.data();
    } else {
      return null;
    }
    final data = await FirebaseFirestore.instance
        .collection('users')
        .doc(userRef.id)
        .get();

    if (data.exists) {
      UserModel user = UserModel.fromMap(data.data()!);
      return user;
    }
  }

    late final future = getData();

   Widget buildprofileheader() {
    
    return FutureBuilder<UserModel?>(future:future,
    builder: ((context, snapshot) {
      if(!snapshot.hasData){
      UserModel user=UserModel.fromMap(userRef.parameters);
      return Padding(padding:EdgeInsets.all(16.0),
      child: Column(
        children: [
                  Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Icon(Icons.account_circle, size: 90,)
            ],
          ),
          Container(
            alignment: Alignment.center,
            padding: EdgeInsets.all(12.0),
            child: Text(
              user.Username ?? "defualtVlueNullCase",
              style: TextStyle(
                fontWeight: FontWeight.bold,
                fontSize:17.0,
              ),
            ),
          ),
        ],
      ),
      );} else{
      return CircularProgress();}
    }),
       );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          centerTitle: true,
          title: Text(
            "Profile",
          ),
        ),
        body: ListView(children: <Widget>[
           buildprofileheader(),
        ]));
  }
}

内容的提问来源于stack exchange，提问作者Abderrezak Douba