flutter调取json数据时数据拿到了，但是切换页面时报错

报错如下：

======== Exception caught by widgets library =======================================================
The following NoSuchMethodError was thrown building FutureBuilder<String>(dirty, state: _FutureBuilderState<String>#c8610):
'[]'
Dynamic call of null.
Receiver: null
Arguments: ["count"]

用的是FutureBuilder来获取数据

class ToBeReadPageState extends State<ToBeReadPage> {
  @override
  Widget build(BuildContext context) {
    return FutureBuilder<String> (
      future: DefaultAssetBundle.of(context).loadString("jsons/toberead.json"),

      builder: (BuildContext context, AsyncSnapshot snapshot) {
        var map = json.decode(snapshot.data.toString());
        List _animes = map["data"];
        print(_animes.map((e) => e["DJSJ"]).toList());

        if (snapshot.connectionState != ConnectionState.done) {
          return HomeNoDataPage();
        }
        return ListView(children:
        _animes
            .map((e) => HomeCard(hTitle: e['YWMS'], hContent: e['YWMS'], hName: e['YHNMXM'], hTime: e['DJSJ']))
            .toList(),
        );
      },
    );
  }
}