Flutter 颤振-从json解析数据永远不会完成

我正在尝试从API检索数据列表。
这是API的响应：

{"permission_requests":[{"id":1,"created_at":"2020-11-02","reason":"Aliquid cum autem id reprehenderit quam quis voluptate enim dolorem magnam doloremque et.","status":"cancelled","date":"06 Nov - 10 Nov","note":"Odit a exercitationem iure culpa voluptatem.","is_pending":false,"type_id":7},{"id":5,"created_at":"2020-11-02","reason":"Rerum incidunt explicabo accusantium nemo commodi quos sed et.","status":"refused","date":"13 Oct - 17 Oct","note":"Corporis ad omnis animi.","is_pending":false,"type_id":2},{"id":11,"created_at":"2020-11-02","reason":"Eveniet sed laudantium vitae perspiciatis molestiae sint minus dolores dolor numquam maxime facere deleniti velit.","status":"cancelled","date":"26 Sep","note":"Debitis perferendis officia aliquam dolor recusandae.","is_pending":false,"type_id":7},{"id":14,"created_at":"2020-11-02","reason":"Ut natus corporis necessitatibus et maiores accusamus repudiandae quas commodi consequatur ratione optio velit ducimus aut.","status":"accepted","date":"26 Sep","note":"Unde possimus laudantium doloribus voluptate ullam.","is_pending":false,"type_id":2},{"id":17,"created_at":"2020-11-02","reason":"Ut vel ea minus sint nemo et ex aut repellendus recusandae ex laboriosam sed aliquam veniam voluptas.","status":"pending","date":"26 Sep","note":"Minima ullam itaque quae ex inventore voluptatum.","is_pending":true,"type_id":4},{"id":24,"created_at":"2020-11-02","reason":"Rerum dignissimos est deserunt dolor aliquam qui repellat sequi quasi culpa rerum.","status":"accepted","date":"19 Sep - 2h","note":"Architecto ab inventore id est.","is_pending":false,"type_id":5},{"id":29,"created_at":"2020-11-02","reason":"Quas aspernatur impedit ea porro accusamus quas voluptatem magni temporibus velit error suscipit ab molestias in omnis.","status":"refused","date":"19 Sep - 2h","note":"Sunt beatae sit quia voluptates et enim cumque ut.","is_pending":false,"type_id":5}]}

这是我的代码：

import 'dart:convert';

import 'package:dio/dio.dart';
import 'package:richiesta_permessi/const.dart';
import 'package:shared_preferences/shared_preferences.dart';

import 'package:richiesta_permessi/exceptions/exceptions.dart';
import 'package:richiesta_permessi/models/permission_request.dart';
import 'package:richiesta_permessi/repositories/authentication.dart';

abstract class PermissionRequestsRepository {
  Future<List<PermissionRequestModel>> getPermissionRequests();
  Future<bool> sendCancelRequest(String permissionRequestId);
}

class RestPermissionRequestsRepository extends PermissionRequestsRepository {
  List<PermissionRequestModel> permissionRequests;
  var httpClient = new Dio();

  @override
  Future<List<PermissionRequestModel>> getPermissionRequests() async {
    try {
      Future<SharedPreferences> _prefs = SharedPreferences.getInstance();
      final SharedPreferences prefs = await _prefs;
      String token = prefs.getString('user_token') ?? null;

      if (null == token) {
        throw PermissionRequestsException(
          message: 'Non è stato possibile recuperare la lista delle richieste',
        );
      }

      httpClient.options.headers['content-Type'] = 'application/json';
      httpClient.options.headers['Authorization'] = 'Bearer $token';
      Response response = await httpClient.get(kGetPermissionRequestsUrl);

      if (response.statusCode != 200) {
        throw PermissionRequestsException(
          message: 'Non è stato possibile recuperare la lista delle richieste',
        );
      }

      final permissionList = response.data['permission_requests'];

      final List<PermissionRequestModel> permissionRequests = permissionList.map((value) => PermissionRequestModel.fromJson(value)).toList();

print('The list is done');
          
      return permissionRequests;
    } catch (e) {
      throw PermissionRequestsException(
        message: 'Non è stato possibile recuperare la lista delle richieste',
      );
    }
  }

  @override
  Future<bool> sendCancelRequest(String permissionRequestId) async {
    try {
      await Future.delayed(Duration(seconds: 1));
      return true;
    } catch (e) {
      throw PermissionRequestsException(
        message: 'Non è stato possibile annullare la richiesta',
      );
    }
  }
}

即使使用此代码，它也不会返回任何内容，如果我使用此代码手动添加数据，它仍然可以工作：

permissionRequests = [
        PermissionRequestModel(
          id: '1',
          reason: 'Lorem ipsum dolor sit amet, consectetur adipiscing elit.',
          status: 'cancelled',
          note: 'Nulla facilisi. Donec mi risus, fringilla a felis ut, auctor placerat leo. Vivamus non placerat eros. Donec quis ullamcorper velit. Vestibulum nec ante efficitur, elementum urna et, feugiat est. Maecenas vel cursus nulla.',
          date: '20 ottobre',
        ),
        PermissionRequestModel(
          id: '2',
          reason: 'In in eros non sapien tempor egestas at nec tellus',
          status: 'refused',
          note: 'Nulla facilisi. Donec mi risus, fringilla a felis ut, auctor placerat leo. Vivamus non placerat eros. Donec quis ullamcorper velit. Vestibulum nec ante efficitur, elementum urna et, feugiat est. Maecenas vel cursus nulla.',
          date: 'Dal 20 al 22 ottobre',
        ),
        PermissionRequestModel(
          id: '3',
          reason: 'Nam ut condimentum dui. Nulla sed ultrices lacus. egestas at nec tellus',
          status: 'pending',
          note: 'Nulla facilisi. Donec mi risus, fringilla a felis ut, auctor placerat leo. Vivamus non placerat eros. Donec quis ullamcorper velit. Vestibulum nec ante efficitur, elementum urna et, feugiat est. Maecenas vel cursus nulla.',
          date: '20 ottobre - 3 ore',
        ),
      ];

这怎么可能？有什么区别

编辑2：

---

好的，当我尝试使用

.add

时，问题是

permissionRequests

，出于某种原因，它只是尝试解析第一个元素，然后永远运行好的，如果有人遇到同样的错误，问题就出在列表的初始化上。
不知道为什么，但这不起作用：

List<PermissionRequestModel> permissionRequests;
permissionRequests.add(Object)

列出许可请求；
permissionRequests.add（对象）

虽然这样做有效：

List<PermissionRequestModel> permissionRequests = []; 
permissionRequests.add(Object)

List permissionRequests=[]；
permissionRequests.add（对象）

好的，如果任何人出现相同的错误，问题在于列表的初始化。
不知道为什么，但这不起作用：

List<PermissionRequestModel> permissionRequests;
permissionRequests.add(Object)

列出许可请求；
permissionRequests.add（对象）

虽然这样做有效：

List<PermissionRequestModel> permissionRequests = []; 
permissionRequests.add(Object)

List permissionRequests=[]；
permissionRequests.add（对象）