How to resolve The operator '[]' isn't defined for the type 'Object'?

Question

Currently working on Grocery Application but getting an error: The operator '[]' isn't defined for the type 'Object'. Tried searching online but got no solution. Flutter Developers help me resolve the error.

import 'package:cloud_firestore/cloud_firestore.dart';

class UserModel{
  static const NUMBER = 'number';
  static const ID = 'id';

  late String _number;
  late String _id;

  String get number => _number;
  String get id => _id;

  UserModel.fromSnapShot(DocumentSnapshot documentSnapshot){
    _number = documentSnapshot.data()![NUMBER];
    _id = documentSnapshot.data()![ID];
  }
}

UPDATE: ERROR FIXED

import 'package:cloud_firestore/cloud_firestore.dart';

class UserModel{
  static const NUMBER = 'number';
  static const ID = 'id';

  String? _number;
  String? _id;

  String? get number => _number;
  String? get id => _id;

  UserModel.fromSnapShot(DocumentSnapshot<Map<String,dynamic>> documentSnapshot){
    _number = documentSnapshot.data()![NUMBER];
    _id = documentSnapshot.data()![ID];
  }
}