How to play list(array) of videos from firebase :In my case I tried with lot of changes but I get this error

Question

Here there are my two Dart file from that I retrieve my Video from firestore but in that, I made video array and try to retrieve it but it gives me an error , if I am doing it with string instead of array It looks fine but in my project, I am requiring array so please help me to finger out.

My cloud firestore looks like is: collection(Course)=>autoid=>doucuments(video array)=>([0]url [1]url2)

Here is my 2 Dart file please correct my code what is wrong in this case when I am running this I got error Like :

Error: list is not a subtype of type 'string'.

code:main.dart and chewie_list_item.dart

     main.dart:It is for retrieve data

   import 'chewie_list_item.dart';
        import 'package:flutter/foundation.dart';
        import 'package:flutter/material.dart';
        import 'package:cloud_firestore/cloud_firestore.dart';`enter code here`
        import 'package:video_player/video_player.dart';
        
        void main() {
          FlutterError.onError = (FlutterErrorDetails details) {
            FlutterError.dumpErrorToConsole(details);
            if (kReleaseMode) exit(1);
          };
        
          runApp(MaterialApp(
            home: CourseApp(),
          ));
        }
        
        class CourseApp extends StatelessWidget {
          // This widget is the root of your application.
          @override
          Widget build(BuildContext context) {
            return Scaffold(
                appBar: AppBar(
                  title: Text("Flutter Demo"),
                ),
                body: StreamBuilder(
                  stream: Firestore.instance.collection("courses").snapshots(),
                  builder: (context, snapshot) {
                    return ListView.builder(
                      itemCount: snapshot.data.documents.length,
                      itemBuilder: (context, index) {
                        DocumentSnapshot courses = snapshot.data.documents[index];
                        return (ChewieListItem(
                          videoPlayerController: VideoPlayerController.network(
                              courses['video'] ?? 'default'),
                        ));
                      },
                    );
                  },
                ));
          }
        }
        
        [code 2: chewie_list_item.dart]: It for chewie video player. 
        
        import 'package:chewie/chewie.dart';
        import 'package:flutter/material.dart';
        import 'package:video_player/video_player.dart';
        
        class ChewieListItem extends StatefulWidget {
          // This will contain the URL/asset path which we want to play
          final VideoPlayerController videoPlayerController;
          final bool looping;
        
          ChewieListItem({
            @required this.videoPlayerController,
            this.looping,
            Key key,
          }) : super(key: key);
        
          @override
          _ChewieListItemState createState() => _ChewieListItemState();
        }
        
        class _ChewieListItemState extends State<ChewieListItem> {
          ChewieController _chewieController;
        
          @override
          void initState() {
            super.initState();
            // Wrapper on top of the videoPlayerController
            _chewieController = ChewieController(
              videoPlayerController: widget.videoPlayerController,
              aspectRatio: 16 / 9,
              // Prepare the video to be played and display the first frame
              autoInitialize: true,
              looping: widget.looping,
              // Errors can occur for example when trying to play a video
              // from a non-existent URL
              errorBuilder: (context, errorMessage) {
                return Center(
                  child: Text(
                    errorMessage,
                    style: TextStyle(color: Colors.white),
                  ),
                );
              },
            );
          }
        
          @override
          Widget build(BuildContext context) {
            return Padding(
              padding: const EdgeInsets.all(8.0),
              child: Chewie(
                controller: _chewieController,
              ),
            );
          }
        
          @override
          void dispose() {
            super.dispose();
            // IMPORTANT to dispose of all the used resources
            widget.videoPlayerController.dispose();
            _chewieController.dispose();
          }
        }
    
    

So mainly I have not any idea hoe to retrieve this video array from my firebase please give the correct code.