FireStore Issue - getting instance of Document on builder callback

fireStoreTest.dart

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/material.dart';
import 'package:flutter/painting.dart';
import 'package:flutter/widgets.dart';
import 'package:flutter_tic_tac_toe/storage/game_info_repository.dart';

class VictoriesList extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    Firestore.instance
        .collection('books')
        .document()
        .setData({'title': 'title', 'author': 'author'});

    return StreamBuilder<QuerySnapshot>(
        stream: Firestore.instance
            .collection(GameInfoRepository.VICTORIES_DOC_NAME)
            .snapshots(),
        builder: (context, snapshot) {
          if (snapshot.hasError) {
            return new Text('Error: ${snapshot.error}',
                textDirection: TextDirection.ltr);
          }
          switch (snapshot.connectionState) {
            case ConnectionState.waiting:
              return new Text(
                'Loading...',
                textDirection: TextDirection.ltr,
              );
            default:
              if (!snapshot.hasData) {
                print("No Data");
                return new Text(
                  "No Data",
                  textDirection: TextDirection.ltr,
                );
              }
              return new ListView(
                children:
                    snapshot.data.documents.map((DocumentSnapshot document) {
                  print("-----------Document:$document" + document.toString());
                  return new ListTile(
                    title: new Text(document['title']),
                    subtitle: new Text(document['author']),
                  );
                }).toList(),
              );
          }
        });
  }
}

I am facing this Issue. Below is the output.
I have written bold text of print statement on line 41.

Performing hot reload...
Syncing files to device ONEPLUS A6000...
D/DecorView(27652): onWindowFocusChangedFromViewRoot hasFocus: true, DecorView@eb74a17[MainActivity]
Reloaded 2 of 508 libraries in 4,885ms.
I/flutter (27652): -----------Document:Instance of 'DocumentSnapshot'Instance of 'DocumentSnapshot'

════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
The following assertion was thrown building StreamBuilder(dirty, state: _StreamBuilderBaseState<QuerySnapshot, AsyncSnapshot>#75baa):
A non-null String must be provided to a Text widget.
'package:flutter/src/widgets/text.dart':
Failed assertion: line 298 pos 10: 'data != null'

The relevant error-causing widget was:
StreamBuilder file:///home/akhil-kfn/AndroidStudioProjects/flutter-tic-tac-toe/lib/storage/fireStore.dart:15:12
When the exception was thrown, this was the stack:
#2 new Text (package:flutter/src/widgets/text.dart:298:10)
#3 VictoriesList.build.. (package:flutter_tic_tac_toe/storage/fireStore.dart:43:32)
#4 MappedListIterable.elementAt (dart:_internal/iterable.dart:417:31)
#5 ListIterable.toList (dart:_internal/iterable.dart:221:19)
#6 VictoriesList.build. (package:flutter_tic_tac_toe/storage/fireStore.dart:46:20)
...
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