title: A build function returned null,The offending widget is: BlocBuilder<NotificationBloc, NotificationState> in flutter_bloc package
body: <p>I am a beginner in flutter as well as in flutter_bloc where i'm trying to get the widget in blocbuilder but getting the "A build function returned null. The offending widget is:BlocBuilder. Build functions must never return null." Below is the bloc code and also the null error which is from console.</p>
  
  <pre><code>        Column(
            children: &lt;Widget&gt;[
              Container(
                color: Colors.white,
                child: BlocListener&lt;NotificationBloc, NotificationState&gt;(
                  listener: (context, state) {
                  },
                  child: BlocBuilder&lt;NotificationBloc, NotificationState&gt;(
                    builder: (context, state) {
                      if (state is NotificationLoadedState) {
                        return NotificationIconBuild();
                      }
                    },
                  ),
                ),
              )
            ],
          )
    Widget NotificationIconBuild() {
      return Column(
        children: &lt;Widget&gt;[
          IconButton(
            icon: Icon(Icons.notifications),
            onPressed: () {},
          ),
          IconButton(
            icon: Icon(Icons.notifications),
            onPressed: () {},
          ),])}
  </code></pre>
  
  <blockquote>
    <p>Error from console log</p>
  </blockquote>
  
  <pre><code>I/flutter (13632): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
  I/flutter (13632): The following assertion was thrown building BlocBuilder&lt;NotificationBloc, NotificationState&gt;(dirty,
  I/flutter (13632): state: _BlocBuilderBaseState&lt;NotificationBloc, NotificationState&gt;#7fa62):
  I/flutter (13632): A build function returned null.
  I/flutter (13632): The offending widget is:
  I/flutter (13632):   BlocBuilder&lt;NotificationBloc, NotificationState&gt;
  I/flutter (13632): Build functions must never return null.
  I/flutter (13632): To return an empty space that causes the building widget to fill available room, return
  I/flutter (13632): "Container()". To return an empty space that takes as little room as possible, return
  I/flutter (13632): "Container(width: 0.0, height: 0.0)".
  I/flutter (13632): 
  I/flutter (13632): The relevant error-causing widget was:
  I/flutter (13632):   BlocBuilder&lt;NotificationBloc, NotificationState&gt;
  I/flutter (13632):   file:///C:/Users/Nabil/AndroidStudioProjects/flutter_save/lib/home_page.dart:77:24
  </code></pre>