Unhandled Exception: type '_Map<String, dynamic>' is not a subtype of type 'Contact_Item'

안녕하세요. 강의를 듣고나서 테스트를 해보는데 안되어서 문의 좀 드립니다.

addrinfo: json['addrinfo'] == null ? null : List<Contact_Item>.from(json['addrinfo']),

위 부분을 어떻게 처리해야 해결될 수 있는지를 모르겠습니다.

addrinfo 는 값이 서버에서 null을 반환할 수도 있고

List<Contact_Item> 을 반환할 수도 있습니다.

class Contact_Item {
  final String idx;
  final String userNM;
  final String mobileNO;
  final String telNO;
  final String photo;
  final bool checkBoxState;

  const Contact_Item({
    required this.idx,
    required this.userNM,
    required this.mobileNO,
    required this.telNO,
    required this.photo,
    required this.checkBoxState,
  });

  factory Contact_Item.fromJson(Map<String, dynamic> json) {
    return Contact_Item(
      idx: json['idx'] as String,
      userNM: json['userNM'] as String,
      mobileNO: json['mobileNO'] as String,
      telNO: json['telNO'] as String,
      photo: json['photo'] as String,
      checkBoxState: json['checkBoxState'] as bool,
    );
  }

}

class ContactResult {
  final String status;
  final String message;
  final List<Contact_Item>? addrinfo;

  const ContactResult({
    required this.status,
    required this.message,
    this.addrinfo,
  });

  factory ContactResult.fromJson(Map<String, dynamic> json) {
    return ContactResult(
      status: json['status'] ?? '',
      message: json['message'] ?? '',
      addrinfo: json['addrinfo'] == null ? null : List<Contact_Item>.from(json['addrinfo']),
    );
  }
}

abstract class ContactRepo {
  Future<ContactResult> getAddressData(ContactRequest req);
}

class ContactService extends ContactRepo {

  Future<ContactResult> getAddressData(ContactRequest req) async {
    BaseOptions options = BaseOptions(
      baseUrl: RetrofitURL.baseUrl,
    );
    Dio dio = Dio(options);
    dio.interceptors.add(Logging());

    FormData formData = FormData.fromMap({
      "keyword": req.keyword,
      "search": req.search,
    });

    final response = await dio.post(RetrofitURL.contactData, data: formData);
    print(response);
    // print(response.data.runtimeType);
    //print(response.headers);
    if (response.statusCode == 200) {
      ContactResult result = ContactResult.fromJson(response.data);
      return result;
    } else {
      return ContactResult(status: "fail", message: "fail", addrinfo: null);
    }
  }
}

에러 메시지 내용

I/flutter (23550): RESPONSE[200] => PATH: /androidSample/ContactList.php

I/flutter (23550): {"status":"success","message":"","addrinfo":[{"idx":1,"userNM":"개발자","mobileNO":"01000010001","telNO":"0234560001","photo":"1.jpg","checkBoxState":false},{"idx":2,"userNM":"이정은","mobileNO":"01001230001","telNO":"","photo":"2.jpg","checkBoxState":false},{"idx":3,"userNM":"김홍길","mobileNO":"01001230002","telNO":"","photo":"null","checkBoxState":false},{"idx":4,"userNM":"최신형","mobileNO":"01001230003","telNO":"","photo":"4.jpg","checkBoxState":false},{"idx":5,"userNM":"홍길동","mobileNO":"01000009880","telNO":"","photo":"5.jpg","checkBoxState":false},{"idx":6,"userNM":"김아정","mobileNO":"01001230005","telNO":"","photo":null,"checkBoxState":false},{"idx":7,"userNM":"이순신","mobileNO":"01001230006","telNO":"","photo":"7.jpg","checkBoxState":false},{"idx":8,"userNM":"이정민","mobileNO":"01000010887","telNO":"","photo":null,"checkBoxState":false},{"idx":9,"userNM":"최재수","mobileNO":"01001110000","telNO":"","photo":"9.jpg","checkBoxState":false},{"idx":10,"userNM":"장정은"

E/flutter (23550): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: type '_Map<String, dynamic>' is not a subtype of type 'Contact_Item'

E/flutter (23550): #0 new List.from (dart:core-patch/array_patch.dart:29:5)

E/flutter (23550): #1 new ContactResult.fromJson (package:login_ex/contact/model/contact_result.dart:19:51)

E/flutter (23550): #2 ContactService.getAddressData (package:login_ex/contact/repository/contact_service.dart:32:44)

E/flutter (23550): <asynchronous suspension>

E/flutter (23550): #3 MainScreenState.getContactData (package:loginex/contact/view/main_screen.dart:35:30)

E/flutter (23550): <asynchronous suspension>

addrinfo: json['addrinfo'] == null ? null : json['addrinfo'].map<Contact_Item>((i) => Contact_Item.fromJson(i)).toList(),