title: Flutter error - failed assertion: line 213 pos 15: 'data != null': is not true at the time of fetching data from firestore
body: <p>Working on Android app using flutter. Trying to fetch documents from firestore &amp; show on the screen through a widget. Here is my code...</p>
  
  <pre><code>import 'dart:async';
  import 'dart:io';
  import 'package:flutter/material.dart';
  import 'package:shared_preferences/shared_preferences.dart';
  import 'package:image_picker/image_picker.dart';
  import 'package:firebase_storage/firebase_storage.dart';
  import 'package:cloud_firestore/cloud_firestore.dart';
  import 'package:http/http.dart' as http;
  import 'dart:convert';
  
  class HomePage extends StatefulWidget {
    @override
    HomePageState createState() =&gt; new HomePageState();
  }
  
  class HomePageState extends State&lt;HomePage&gt; {
  
    @override
    void initState() {
      super.initState();
    }
  
  
  
    @override
    Widget build(BuildContext context) {
  
      Widget userTimeline = new Container(
          margin: const EdgeInsets.only(top: 30.0, right: 20.0, left: 20.0),
          child: new Row(
            children: &lt;Widget&gt;[
              new Expanded(
                  child: new Column(
                children: &lt;Widget&gt;[
                  new StreamBuilder&lt;QuerySnapshot&gt;(
                    stream: Firestore.instance.collection('tripsDocs').snapshots(),
                    builder: (BuildContext context, AsyncSnapshot&lt;QuerySnapshot&gt; snapshot) {
                      if (!snapshot.hasData) return new Text('Loading...');
  
                      new ListView(
                        children: snapshot.data.documents.map((DocumentSnapshot document) {
                          new ListTile(
                            title: document['docTitle'] != null? new Text(document['docTitle']) : new Text("Hello"),
                            subtitle: new Text('Suresh'),
                          );
                        }).toList(),
                      );
                    },
                  )
                ],
              ))
            ],
          ));
  
      return new Scaffold(
  
        body: new ListView(
          children: &lt;Widget&gt;[
            userTimeline,
          ],
        ),
  
      );
  
    }
  }
  </code></pre>
  
  <p>But, whenever I'm executing this widget I'm getting following error...</p>
  
  <pre><code>'package:flutter/src/widgets/text.dart': Failed assertion: line 213 pos 15: 'data != null': is not true
  </code></pre>
  
  <p>Can't able to understand what's going wrong. </p>