title: While I am retrieving my array of document in cloud firestore using Flutter I got error like list is not a sub type of string
body: <p>Here is my dart code:</p>
  <pre><code>import 'dart:io';
  
  import 'chewie_list_item.dart';
  import 'package:flutter/foundation.dart';
  import 'package:flutter/material.dart';
  import 'package:cloud_firestore/cloud_firestore.dart';
  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(&quot;Flutter Demo&quot;),
          ),
          body: StreamBuilder(
            stream: Firestore.instance.collection(&quot;courses&quot;).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></pre>
  <p><a href="https://i.stack.imgur.com/E2INC.png" rel="nofollow noreferrer">This is the error message I get</a> while running the app and <a href="https://i.stack.imgur.com/uwykU.png" rel="nofollow noreferrer">this is my firestore structure</a>.</p>