DartPad issue: WidgetSpan is not showing.

widgetspan_broken_on_dartpad.dart

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Text.rich(
        WidgetSpan(child: Text('Broken!')),
//         TextSpan(text: 'Works!'),
      ),
    );
  }
}