我试图从 JSON 获取信息，但我遇到了问题。
这是 JSON 文件：

{
    "version": "v1",
    "resource": "***",
    "action": "show",
    "method": "GET",
    "query": {
        "type": "list",
        "query": null,
        "pagination": null
    },
    "request": [],
    "data": {
        "Total": [
            {
                "id": 34724,
                "rank": 1,
                "loss": 0,
             }
           ....
        ],
        "Away": [
             {
              "id": 3125"
              "rank": 0"
              }
           ....
        ]
   }
}

这就是我试图解码它并存储数据的方式：

class Standings {
  final String version;
  final String resource;
  final String action;
  final String method;
   List<Data> datas;

  Standings(
      {this.version, this.resource, this.action, this.method,         this.datas});

  factory Standings.fromJson(Map<String, dynamic> parsedJson) {

    var listD = parsedJson['data'];
    print(listD.runtimeType);
    List<Data> dataList = listD.map((i) => Data.fromJson(i)).toList();

    return Standings(
        version: parsedJson['version'],
        resource: parsedJson['resource'],
        action: parsedJson['action'],
        method: parsedJson['method'],
        datas: dataList,
    );
  }
}
class Data {
  List<Total> total;
  List<Away> away;

  Data(
      {this.total, this.away});

  factory Data.fromJson(Map<String, dynamic> parsedJson) {

    var listT = parsedJson['Total'] as List;
    print(listT.runtimeType);
    List<Total> totalList = listT.map((i) => Total.fromJson(i)).toList();

    var listA = parsedJson['Away'] as List;
    print(listA.runtimeType);
    List<Away> awayList = listA.map((i) => Away.fromJson(i)).toList();

    return Data(
        total: totalList,
        away: awayList,
        );
  }
}
class Total {
  final int id;
  final int rank;
  final int loss;

  Total({
    this.id,
    this.rank,
    this.loss,        
  });

  factory Total.fromJson(Map<String, dynamic> parsedJson) {
    return Total(
      id: parsedJson['id'],
      rank: parsedJson['rank'],
      loss: parsedJson['loss'],
   ); 
   }
 }

和同样的事情，但我得到这个错误：

数据在 null 上调用
I/flutter(14264)：══╡WIDGETS LIBRARY 的例外情况
╞═════════════════════════════════════════════════ ══════════
I/flutter(14264)：抛出以下 NoSuchMethodError 构建
Schedule(dirty，州：
I/flutter(14264)：_ScheduleState#2dfb0(ticker inactive))：
I/flutter(14264)：getter'datas'在 null 上调用。
I/flutter(14264)：接收者：null
I/flutter(14264)：尝试呼叫：数据

我该怎么做才能解决这个问题？

json http flutter