[Dúvida] Tentando adicionar o BottomAppBar da documentação

import 'package:flutter/material.dart';

void main() {
  runApp(const BottomAppBarDemo());
}

class BottomAppBarDemo extends StatefulWidget {
  const BottomAppBarDemo({super.key});

  @override
  State createState() => _BottomAppBarDemoState();
}

class _BottomAppBarDemoState extends State<BottomAppBarDemo> {
  bool _showFab = true;
  bool _showNotch = true;
  FloatingActionButtonLocation _fabLocation =
      FloatingActionButtonLocation.endDocked;

  void _onShowNotchChanged(bool value) {
    setState(() {
      _showNotch = value;
    });
  }

  void _onShowFabChanged(bool value) {
    setState(() {
      _showFab = value;
    });
  }

  void _onFabLocationChanged(FloatingActionButtonLocation? value) {
    setState(() {
      _fabLocation = value ?? FloatingActionButtonLocation.endDocked;
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          backgroundColor: Color.fromARGB(100, 0, 128, 0),
          automaticallyImplyLeading: false,
          title: const Text('Casamento'),
        ),
        body: Card(
          child: ListTile(
            leading: Icon(Icons.monetization_on),
            title: Text('100.0'),
            subtitle: Text('1000'),
          ),
        ),
        floatingActionButton: _showFab
            ? FloatingActionButton(
                onPressed: () {},
                tooltip: 'Create',
                backgroundColor: Color.fromARGB(100, 0, 128, 0),
                child: const Icon(Icons.add),
              )
            : null,
        floatingActionButtonLocation: _fabLocation,
        bottomNavigationBar: _DemoBottomAppBar(
          fabLocation: _fabLocation,
          shape: _showNotch ? const CircularNotchedRectangle() : null,
        ),
      ),
    );
  }
}

class _DemoBottomAppBar extends StatelessWidget {
  const _DemoBottomAppBar({
    this.fabLocation = FloatingActionButtonLocation.endDocked,
    this.shape = const CircularNotchedRectangle(),
  });

  final FloatingActionButtonLocation fabLocation;
  final NotchedShape? shape;

  static final List<FloatingActionButtonLocation> centerLocations =
      <FloatingActionButtonLocation>[
    FloatingActionButtonLocation.centerDocked,
    FloatingActionButtonLocation.centerFloat,
  ];

  @override
  Widget build(BuildContext context) {
    return BottomAppBar(
      shape: shape,
      color: Color.fromARGB(100, 0, 128, 0),
      child: IconTheme(
        data: IconThemeData(color: Theme.of(context).colorScheme.onPrimary),
        child: Row(
          children: <Widget>[
            IconButton(
              tooltip: 'Open navigation menu',
              icon: const Icon(Icons.menu),
              onPressed: () {},
            ),
            if (centerLocations.contains(fabLocation)) const Spacer(),
            IconButton(
              tooltip: 'Search',
              icon: const Icon(Icons.search),
              onPressed: () {},
            ),
            IconButton(
              tooltip: 'Favorite',
              icon: const Icon(Icons.favorite),
              onPressed: () {},
            ),
          ],
        ),
      ),
    );
  }
}

Não aparece o ícone ou o texto