问题是null安全和迁移如何解决运算符'[]‘没有为类型'Object’定义 导入'package:cloud_firestore/cloud_firestore.dart'; 类UserModellate String _id; //getter String get number => _number; String get id => _id; UserModel.fromSnapshot(DocumentSnapshot</
AsyncSnapshot snapshot) { var userDocument = snapshot.data as DocumentSnapshotText("none"); } }The getter 'length' isn't defined for the type 'DocumentSnapshot