我无法理解如何使用以下语句返回null：下面是一个简单的方法：

@override
  Future<People> searchPeople({required String email}) async {
    var user = auth.FirebaseAuth.instance.currentUser;
    final docs = await FirebaseFirestore.instance
        .collection('users')
        .doc(user!.email)
        .collection('people')
        .where('hunting', isEqualTo: email)
        .get();

    final docData = docs.docs.map((doc) {
      return People.fromSnapshot(doc);
    });

    var res = docData.firstWhere(
      (element) => element.hunting == email,
      orElse: () => null, // The return type 'Null' isn't a 'People', as required by the closure's 
    );
    print(res);
    return res;
  }

问题是它抛出错误：* 返回类型"Null"不是闭包所要求得"People"*
我已经在这里读了很多答案，但是所有的例子和答案都只适用于返回类型string，int，等等...当类型是一个对象（People）时，如何处理null？已经尝试过使用集合：firstWhereOrNull，但错误仍然存在...
我的模型中是否有需要更改的地方？

class People extends Equatable {
  String? hunting;
  String? username;
  String? persona;

  People({
    this.hunting,
    this.username,
    this.persona,
  });

  @override
  List<Object?> get props => [hunting, username, persona];
  static People fromSnapshot(DocumentSnapshot snapshot) {
    People people = People(
      hunting: snapshot['hunting'],
      username: snapshot['username'],
      persona: snapshot['persona'],
    );
    return people;
  }

  Map<String, dynamic> toMap() {
    return {
      'hunter': hunting,
      'username': username,
      'persona': persona,
    };
  }
}

谢谢你的帮助!