title: The method '>' was called on null
body: <p>Why i have this error whereas all variables is iniatialize.</p>
  
  <blockquote>
    <p>════════ Exception caught by rendering library ═════════════════════════════════
    RenderBox was not laid out: _RenderLayoutBuilder#657cb relayoutBoundary=up1 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
    'package:flutter/src/rendering/box.dart':
    Failed assertion: line 1681 pos 12: 'hasSize'
    User-created ancestor of the error-causing widget was
        Scaffold 
    ════════ Exception caught by rendering library ═════════════════════════════════
    The method '>' was called on null.
    Receiver: null
    Tried calling: >(1e-10)
    User-created ancestor of the error-causing widget was
        OrientationBuilder 
    lib\no_events.dart:31
    ═══════════════════════</p>
  </blockquote>
  
  <pre><code>class _NoEvents extends State&lt;NoEvents&gt; {
    List&lt;Contributor&gt; contributors = [];
    List&lt;Event&gt; events = [];
    Contributor contributor = new Contributor(1, "XXX");
  
    @override
    Widget build(BuildContext context) {
      contributors.add(contributor);
      Event event1 = new Event(1, contributors, DateTime(2019 - 10 - 25), "XXX", "Test1");
      Event event2 = new Event(1, contributors, DateTime.now(), "XXX", "Test2");
      Event event3 = new Event(1, contributors, DateTime.now(), "XXX", "Test3");
      events.add(event1);
      events.add(event2);
      events.add(event3);
  
      return Scaffold(
        appBar: AppBar(
          title: new Text('Lille Events'),
        ),
        body: new OrientationBuilder(
          builder: (context, orientation) {
            return new Column(
              children: &lt;Widget&gt;[
                new GridView.count(
                  crossAxisCount: orientation == Orientation.portrait ? 2 : 3,
                  children: &lt;Widget&gt;[
                    for (var e in events)
                      new Center(
                        child: new Text(e.subject),
                      ),
                  ],
                ),
              ],
            );
          },
        ),
      );
    }
  }
  
  </code></pre>