常連

### 前提・実現したいこと

youtube data apiのvideosからデータを取得してfirestoreにデータを入れるということがしたいです。
エラーの内容をググると
home_screen.dart
```
Future<VideoItem> _loadVideos() async {
    VideosList _videosList = await Services.getVideosList(
      videosId: _videosId,
    );
    setState(() {});
    return _videosList.videoItems[0];
  }
```
ここのreturnの部分でvideoItems[0]がnullになってしまっているのかなと予想します。間違っているかもしれませんが。
もしそうならvideos_list.dartの中のどこかが間違っているんだろうなとは思っているんですが、分かりません。
videoItemsの値を取得するにはどうすればいいですか？
flutter勉強し始めて２週間で基礎がわかっていない部分が多くありますがご容赦ください。
足りない情報あれば追記します。
### 発生している問題・エラーメッセージ

```
[VERBOSE-2:ui_dart_state.cc(186)] Unhandled Exception: NoSuchMethodError: The method 'map' was called on null.
Receiver: null
Tried calling: map(Closure: (dynamic) => VideoItem)
#0      Object.noSuchMethod (dart:core-patch/object_patch.dart:54:5)
#1      new VideosList.fromJson (package:nanashi_schedule/models/videos_list.dart:27:48)
#2      videosListFromJson (package:nanashi_schedule/models/videos_list.dart:7:57)
#3      Services.getVideosList (package:nanashi_schedule/utils/services.dart:49:29)
<asynchronous suspension>
#4      _HomeScreenState._loadVideos (package:nanashi_schedule/screens/home_screen.dart:179:30)
<asynchronous suspension>
#5      _HomeScreenState._getSearchInfo (package:nanashi_schedule/screens/home_screen.dart:109:31)
<asynchronous suspension>

```

### 該当のソースコード
home_screen.dart
```ここに言語名を入力
import 'package:cached_network_image/cached_network_image.dart';
import 'package:flutter/material.dart';
import 'package:nanashi_schedule/models/search_info.dart';
import 'package:nanashi_schedule/models/videos_list.dart';
import 'package:nanashi_schedule/utils/services.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:url_launcher/url_launcher.dart';

class HomeScreen extends StatefulWidget {
  @override
  _HomeScreenState createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  //
  final List list = [
    ["https://yt3.ggpht.com/ytc/AAUvwngvgRbvQSxZHcosptXrl6PO3djyKHY7ZLIGbQHo=s176-c-k-c0x00ffffff-no-rj", "UC0Owc36U9lOyi9Gx9Ic-4qg"],
    ["https://yt3.ggpht.com/ytc/AAUvwnj2XS4F6MS5aaKGDaQ4mcrPlW44lEN-p9oXqj9x=s176-c-k-c0x00ffffff-no-rj", "UC2kyQhzGOB-JPgcQX9OMgEw"],
    ["https://yt3.ggpht.com/ytc/AAUvwnit824wjmPA7AE7LDtG0EVjmutNl4-sICtStfTh=s176-c-k-c0x00ffffff-no-rj", "UCRvpMpzAXBRKJQuk-8-Sdvg"],
    ["https://yt3.ggpht.com/ytc/AAUvwngUM0DtcqRxbIHvfd8t3D-YEFLudJbN29dpdy44=s176-c-k-c0x00ffffff-no-rj", "UCXp7sNC0F_qkjickvlYkg-Q"],
    ["https://yt3.ggpht.com/ytc/AAUvwnhkL2lOLKPB4cqpPgqjHDV9AVypXtkNt10Eqm0=s176-c-k-c0x00ffffff-no-rj", "UCW8WKciBixmaqaGqrlTITRQ"],
  ];

  //
  SearchInfo _searchInfo;
  VideosList _videosList;
  Item _item;
  bool _loading;
  String _videosId;



  @override
  void initState() {
    super.initState();
    _loading = true;
    _videosList = VideosList();
    _videosList.videoItems = [];
  }

  Future<void> _getSearchInfo(List<dynamic> list) async {
    for(int i = 0; i < list.length; i++) {
      _searchInfo = await Services.searchInfo(channelId: list[i][1]);
      print(_searchInfo.items.length);
      for(int itemIndex = 0; itemIndex < _searchInfo.items.length; i++) {
        print('do');
        _item = _searchInfo.items[itemIndex];
        _videosId = _item.id.videoId;
        print('${list[i][0]}  =======_videosId: $_videosId');
        print('get a video');
        VideoItem videoItem = await _loadVideos();
        print('success get video info');
        
        var documentID = _videosId;
        Firestore.instance.collection('videos')
            .document(documentID)
            .snapshots()
            .listen((snapshot) {
          if (!snapshot.exists) {
            //登録されてない新しいドキュメント
            debugPrint('iconUrl: '+ list[i][0]);
            debugPrint('channelTitle: '+ videoItem.videosnippet.channelTitle);
            String tes = '公開時間：${videoItem.liveStreamingDetails.scheduledStartTime.hour}:${videoItem.liveStreamingDetails.scheduledStartTime.minute}';
            debugPrint(tes);
            debugPrint('thumbnailUrl: '+ videoItem.videosnippet.thumbnails
                .thumbnailsDefault.url);
            debugPrint('title: '+ videoItem.videosnippet.title);
            debugPrint('videoUrl: '+ _videosId);
            debugPrint('channelUrl: '+list[i][1]);

            Firestore.instance.collection('videos')
                .document(documentID)
                .setData(
                {
                  'iconUrl': list[i][0],
                  'channelTitle': videoItem.videosnippet.channelTitle,
                  'scheduledStartTime': videoItem.liveStreamingDetails
                      .scheduledStartTime,
                  'thumbnailUrl': videoItem.videosnippet.thumbnails
                      .thumbnailsDefault.url,
                  'title': videoItem.videosnippet.title,
                  'videoUrl': 'https://www.youtube.com/watch?v=' + _videosId,
                  'channelUrl': 'https://www.youtube.com/channel/' + list[i][1],
                }
            );
          } else {
            Firestore.instance.collection('videos')
                .document(documentID)
                .updateData(
                {
                  'iconUrl': list[i][0],
                  'channelTitle': videoItem.videosnippet.channelTitle,
                  'scheduledStartTime': videoItem.liveStreamingDetails
                      .scheduledStartTime,
                  'thumbnailUrl': videoItem.videosnippet.thumbnails
                      .thumbnailsDefault.url,
                  'title': videoItem.videosnippet.title,
                  'videoUrl': 'https://www.youtube.com/watch?v=' + _videosId,
                  'channelUrl': 'https://www.youtube.com/channel/' + list[i][1],
                }
            );
          }
        });
      }
    }
    print('setstate');
    setState(() {
      _loading = true;
    });
  }

  Future<VideoItem> _loadVideos() async {
    VideosList _videosList = await Services.getVideosList(
      videosId: _videosId,
    );
    setState(() {});
    return _videosList.videoItems[0];
  }

  @override
  Widget build(BuildContext context) {
以下UI~~~
```

videos_list.dart
```ここに言語を入力
import 'dart:convert';

VideosList videosListFromJson(String str) => VideosList.fromJson(json.decode(str));

String videosListToJson(VideosList data) => json.encode(data.toJson());

class VideosList {
  VideosList({
    this.kind,
    this.etag,
    this.videoItems,
    this.pageInfo,
  });

  String kind;
  String etag;
  List<VideoItem> videoItems;
  PageInfo pageInfo;

  factory VideosList.fromJson(Map<String, dynamic> json) => VideosList(
    kind: json["kind"],
    etag: json["etag"],
    videoItems: List<VideoItem>.from(json["items"].map((x) => VideoItem.fromJson(x))), //new VideosList.fromJson (package:nanashi_schedule/models/videos_list.dart:27:48)
    pageInfo: PageInfo.fromJson(json["pageInfo"]),
  );

  Map<String, dynamic> toJson() => {
    "kind": kind,
    "etag": etag,
    "items": List<dynamic>.from(videoItems.map((x) => x.toJson())),
    "pageInfo": pageInfo.toJson(),
  };
}

class VideoItem {
  VideoItem({
    this.kind,
    this.etag,
    this.id,
    this.videosnippet,
    this.liveStreamingDetails,
  });

  String kind;
  String etag;
  String id;
  VideoSnippet videosnippet;
  LiveStreamingDetails liveStreamingDetails;

  factory VideoItem.fromJson(Map<String, dynamic> json) => VideoItem(
    kind: json["kind"],
    etag: json["etag"],
    id: json["id"],
    videosnippet: VideoSnippet.fromJson(json["snippet"]),
    liveStreamingDetails: LiveStreamingDetails.fromJson(json["liveStreamingDetails"]),
  );

  Map<String, dynamic> toJson() => {
    "kind": kind,
    "etag": etag,
    "id": id,
    "snippet": videosnippet.toJson(),
    "liveStreamingDetails": liveStreamingDetails.toJson(),
  };
}

```
### 試したこと

ここに問題に対して試したことを記載してください。

### 補足情報（FW/ツールのバージョンなど）

ここにより詳細な情報を記載してください。

	@@ -1 +1 @@
1	- ~~Unhandled Exception:~~ NoSuchMethodError: The method 'map' was called on null.
1	+ NoSuchMethodError: The method 'map' was called on null. youtube data apiのvideosからデータを取りたい

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