我正在用flutter制作一个简单的天气应用程序，我使用http包从API获取天气信息。我正在将JSON解析为Dart类，这样我就可以在另一个屏幕上显示它。

这是天气预报类

class FivedayForecastData {
    String cod;
    int message;
    int cnt;
    List<ListElement> list;
    City city;

    FivedayForecastData({
        required this.cod,
        required this.message,
        required this.cnt,
        required this.list,
        required this.city,
    });

    factory FivedayForecastData.fromJson(Map<String, dynamic> json) => FivedayForecastData(
        cod: json["cod"],
        message: json["message"],
        cnt: json["cnt"],
        list: List<ListElement>.from(json["list"].map((x) => ListElement.fromJson(x))),
        city: City.fromJson(json["city"]),
    );

    Map<String, dynamic> toJson() => {
        "cod": cod,
        "message": message,
        "cnt": cnt,
        "list": List<dynamic>.from(list.map((x) => x.toJson())),
        "city": city.toJson(),
    };
}

It says that .map() was called on null even though this 'list' field is not null in the API

这是从API获取数据的函数

required double lattitude,
  required double longitude,
}) async {
  final link =
      'https://api.openweathermap.org/data/2.5/weather?lat=$lattitude&lon=$longitude&appid=$apiKey&units=metric';

  final result = await http.get(Uri.parse(link));
  if (result.statusCode == 200) {
    final data = fivedayForecastDataFromJson(result.body.toString());
    // print(data);
    return data;
  }
}

Part of the JSON data from the API
我仍然在学习和弄清楚http和flutter在geenral的事情，我试图使这个列表为空，只是为了让应用程序运行，但它总是默认为空列表It always defaults to the empty list []