Fix NavigationDrawer selected item has wrong icon color (#129625)
fixes [NavigationDrawer selected item has wrong icon color [Material3 spec]](https://github.com/flutter/flutter/issues/129572)
### Description
This PR fixes a mistake in the `NavigationDrawer` defaults, where generated token value returns a `null`.
This issue can be detected when you want to customize the selected icon color for `NavigationDrawerDestination` using a custom color scheme.
### Code sample
<details>
<summary>expanded to view the code sample</summary>
```dart
import 'package:flutter/material.dart';
void main() => runApp(const MyApp());
class MyApp extends StatelessWidget {
const MyApp({super.key});
@override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
themeMode: ThemeMode.light,
theme: ThemeData(
colorScheme: ColorScheme.fromSeed(seedColor: Colors.blue).copyWith(
onSecondaryContainer: Colors.red,
),
useMaterial3: true,
),
home: const Example(),
);
}
}
class Example extends StatelessWidget {
const Example({super.key});
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('NavigationDrawer Sample'),
),
drawer: const NavigationDrawer(
children: <Widget>[
NavigationDrawerDestination(
icon: Icon(Icons.favorite_outline_rounded),
label: Text('Favorite'),
selectedIcon: Icon(Icons.favorite_rounded),
),
NavigationDrawerDestination(
icon: Icon(Icons.favorite_outline_rounded),
label: Text('Favorite'),
),
],
),
);
}
}
```
</details>
### Before
<img width="1053" alt="Screenshot 2023-06-27 at 13 24 38" src="https://github.com/flutter/flutter/assets/48603081/18c13a73-688f-4586-bb60-bddef45d173f">
### After
<img width="1053" alt="Screenshot 2023-06-27 at 13 24 25" src="https://github.com/flutter/flutter/assets/48603081/8a1427c6-517f-424a-b0bd-24bad7c5fbb0">
7cef966147