title: How to use @required annotation on Flutter constructor parameters?
body: <p>When I annotate a constructor parameter with <code>@required</code> IntelliJ shows an error:</p>
  
  <blockquote>
    <p>Annotation must be either a const variable reference or const constructor invocation</p>
  </blockquote>
  
  <p>Can anyone suggest what I'm doing wrong?</p>
  
  <pre><code>class StatusBar extends StatelessWidget {
    final String text;
  
    const StatusBar({Key key, @required this.text})
        : assert(text != null),
          super(key: key);
  
    @override
    Widget build(BuildContext context) {
      //...
    }
  }
  </code></pre>