🐛 Expander.initiallyExpanded not working

[mgenware]

Describe the bug
Expander.initiallyExpanded does not seem to work. Expander is still collapsed when initiallyExpanded is set to true.

To Reproduce
Steps to reproduce the behavior:

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return ScaffoldPage(
      content: Expander(
          header: Text('Expander'),
          initiallyExpanded: true,
          content: Container(
            height: 100,
            color: Colors.black,
          )),
    );
  }
}

Expected behavior
Expander is expanded when rendered.

Screenshots