Repository: flutter
Issue: GoRouter extra is NULL when pressing browser's back button
Labels: platform-web,package,has reproducible steps,P3,p: go_router,team-go_router,triaged-go_router,found in release: 3.19,found in release: 3.21

### What package does this bug report belong to?

go_router

### What target platforms are you seeing this bug on?

Web

### Have you already upgraded your packages?

Yes

### Dependency versions

<details><summary>pubspec.lock</summary>

```lock
# Generated by pub
# See https://dart.dev/tools/pub/glossary#lockfile
packages:
  async:
    dependency: transitive
    description:
      name: async
      sha256: "947bfcf187f74dbc5e146c9eb9c0f10c9f8b30743e341481c1e2ed3ecc18c20c"
      url: "https://pub.dev"
    source: hosted
    version: "2.11.0"
  boolean_selector:
    dependency: transitive
    description:
      name: boolean_selector
      sha256: "6cfb5af12253eaf2b368f07bacc5a80d1301a071c73360d746b7f2e32d762c66"
      url: "https://pub.dev"
    source: hosted
    version: "2.1.1"
  characters:
    dependency: transitive
    description:
      name: characters
      sha256: "04a925763edad70e8443c99234dc3328f442e811f1d8fd1a72f1c8ad0f69a605"
      url: "https://pub.dev"
    source: hosted
    version: "1.3.0"
  clock:
    dependency: transitive
    description:
      name: clock
      sha256: cb6d7f03e1de671e34607e909a7213e31d7752be4fb66a86d29fe1eb14bfb5cf
      url: "https://pub.dev"
    source: hosted
    version: "1.1.1"
  collection:
    dependency: transitive
    description:
      name: collection
      sha256: ee67cb0715911d28db6bf4af1026078bd6f0128b07a5f66fb2ed94ec6783c09a
      url: "https://pub.dev"
    source: hosted
    version: "1.18.0"
  fake_async:
    dependency: transitive
    description:
      name: fake_async
      sha256: "511392330127add0b769b75a987850d136345d9227c6b94c96a04cf4a391bf78"
      url: "https://pub.dev"
    source: hosted
    version: "1.3.1"
  flutter:
    dependency: "direct main"
    description: flutter
    source: sdk
    version: "0.0.0"
  flutter_lints:
    dependency: "direct dev"
    description:
      name: flutter_lints
      sha256: e2a421b7e59244faef694ba7b30562e489c2b489866e505074eb005cd7060db7
      url: "https://pub.dev"
    source: hosted
    version: "3.0.1"
  flutter_test:
    dependency: "direct dev"
    description: flutter
    source: sdk
    version: "0.0.0"
  flutter_web_plugins:
    dependency: transitive
    description: flutter
    source: sdk
    version: "0.0.0"
  go_router:
    dependency: "direct main"
    description:
      name: go_router
      sha256: "7ecb2f391edbca5473db591b48555a8912dde60edd0fb3013bd6743033b2d3f8"
      url: "https://pub.dev"
    source: hosted
    version: "13.2.1"
  leak_tracker:
    dependency: transitive
    description:
      name: leak_tracker
      sha256: "78eb209deea09858f5269f5a5b02be4049535f568c07b275096836f01ea323fa"
      url: "https://pub.dev"
    source: hosted
    version: "10.0.0"
  leak_tracker_flutter_testing:
    dependency: transitive
    description:
      name: leak_tracker_flutter_testing
      sha256: b46c5e37c19120a8a01918cfaf293547f47269f7cb4b0058f21531c2465d6ef0
      url: "https://pub.dev"
    source: hosted
    version: "2.0.1"
  leak_tracker_testing:
    dependency: transitive
    description:
      name: leak_tracker_testing
      sha256: a597f72a664dbd293f3bfc51f9ba69816f84dcd403cdac7066cb3f6003f3ab47
      url: "https://pub.dev"
    source: hosted
    version: "2.0.1"
  lints:
    dependency: transitive
    description:
      name: lints
      sha256: cbf8d4b858bb0134ef3ef87841abdf8d63bfc255c266b7bf6b39daa1085c4290
      url: "https://pub.dev"
    source: hosted
    version: "3.0.0"
  logging:
    dependency: transitive
    description:
      name: logging
      sha256: "623a88c9594aa774443aa3eb2d41807a48486b5613e67599fb4c41c0ad47c340"
      url: "https://pub.dev"
    source: hosted
    version: "1.2.0"
  matcher:
    dependency: transitive
    description:
      name: matcher
      sha256: d2323aa2060500f906aa31a895b4030b6da3ebdcc5619d14ce1aada65cd161cb
      url: "https://pub.dev"
    source: hosted
    version: "0.12.16+1"
  material_color_utilities:
    dependency: transitive
    description:
      name: material_color_utilities
      sha256: "0e0a020085b65b6083975e499759762399b4475f766c21668c4ecca34ea74e5a"
      url: "https://pub.dev"
    source: hosted
    version: "0.8.0"
  meta:
    dependency: transitive
    description:
      name: meta
      sha256: d584fa6707a52763a52446f02cc621b077888fb63b93bbcb1143a7be5a0c0c04
      url: "https://pub.dev"
    source: hosted
    version: "1.11.0"
  path:
    dependency: transitive
    description:
      name: path
      sha256: "087ce49c3f0dc39180befefc60fdb4acd8f8620e5682fe2476afd0b3688bb4af"
      url: "https://pub.dev"
    source: hosted
    version: "1.9.0"
  sky_engine:
    dependency: transitive
    description: flutter
    source: sdk
    version: "0.0.99"
  source_span:
    dependency: transitive
    description:
      name: source_span
      sha256: "53e943d4206a5e30df338fd4c6e7a077e02254531b138a15aec3bd143c1a8b3c"
      url: "https://pub.dev"
    source: hosted
    version: "1.10.0"
  stack_trace:
    dependency: transitive
    description:
      name: stack_trace
      sha256: "73713990125a6d93122541237550ee3352a2d84baad52d375a4cad2eb9b7ce0b"
      url: "https://pub.dev"
    source: hosted
    version: "1.11.1"
  stream_channel:
    dependency: transitive
    description:
      name: stream_channel
      sha256: ba2aa5d8cc609d96bbb2899c28934f9e1af5cddbd60a827822ea467161eb54e7
      url: "https://pub.dev"
    source: hosted
    version: "2.1.2"
  string_scanner:
    dependency: transitive
    description:
      name: string_scanner
      sha256: "556692adab6cfa87322a115640c11f13cb77b3f076ddcc5d6ae3c20242bedcde"
      url: "https://pub.dev"
    source: hosted
    version: "1.2.0"
  term_glyph:
    dependency: transitive
    description:
      name: term_glyph
      sha256: a29248a84fbb7c79282b40b8c72a1209db169a2e0542bce341da992fe1bc7e84
      url: "https://pub.dev"
    source: hosted
    version: "1.2.1"
  test_api:
    dependency: transitive
    description:
      name: test_api
      sha256: "5c2f730018264d276c20e4f1503fd1308dfbbae39ec8ee63c5236311ac06954b"
      url: "https://pub.dev"
    source: hosted
    version: "0.6.1"
  vector_math:
    dependency: transitive
    description:
      name: vector_math
      sha256: "80b3257d1492ce4d091729e3a67a60407d227c27241d6927be0130c98e741803"
      url: "https://pub.dev"
    source: hosted
    version: "2.1.4"
  vm_service:
    dependency: transitive
    description:
      name: vm_service
      sha256: b3d56ff4341b8f182b96aceb2fa20e3dcb336b9f867bc0eafc0de10f1048e957
      url: "https://pub.dev"
    source: hosted
    version: "13.0.0"
sdks:
  dart: ">=3.3.0 <4.0.0"
  flutter: ">=3.16.0"

```

</details>


### Steps to reproduce

Using the sample code below:
1. Press `Hello World!` to navigate to `SettingsPage`.
2. In `SettingsPage`, press `Hello from Home`. This will push another `SettingsPage`.
3. In the 2nd `SettingsPage`, press browser's back button.

### Expected results

After pressing browser's back button, 1st `SettingsPage`'s extra should not be NULL.

### Actual results

After pressing browser's back button, 1st `SettingsPage`'s extra is NULL.

However, if I set the extra to string, e.g. `extra: 'from Home',`, it's not cleared. Wondering why class extra is being cleared.

### Code sample

<details open><summary>Code sample</summary>

```dart
import 'package:flutter/material.dart';
import 'package:go_router/go_router.dart';

void main() {
  GoRouter.optionURLReflectsImperativeAPIs = true;
  runApp(const MainApp());
}

class MainApp extends StatelessWidget {
  const MainApp({
    super.key,
  });

  @override
  Widget build(BuildContext context) {
    return MaterialApp.router(
      routerConfig: GoRouter(
        initialLocation: '/',
        routes: <RouteBase>[
          GoRoute(
            path: '/',
            builder: (_, __) => const HomePage(),
          ),
          GoRoute(
            path: '/settings',
            builder: (_, state) {
              print('>>>>> settings extra = ${state.extra}');

              return SettingsPage(
                extra: switch (state.extra) {
                  SettingsPageParams(message: final message) => message,
                  _ => state.extra?.toString(),
                },
              );
            },
          ),
        ],
      ),
    );
  }
}

//--------------------------------------------------------------------------------------------------
class HomePage extends StatelessWidget {
  const HomePage({
    super.key,
  });

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: TextButton(
          onPressed: () => context.push(
            '/settings',
            extra: const SettingsPageParams('from Home'),
          ),
          child: const Text('Hello World!'),
        ),
      ),
    );
  }
}

//--------------------------------------------------------------------------------------------------
class SettingsPage extends StatelessWidget {
  const SettingsPage({
    this.extra,
    super.key,
  });

  final String? extra;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: Center(
        child: TextButton(
          onPressed: () => context.push(
            '/settings',
            extra: const SettingsPageParams('from Settings'),
          ),
          child: Text('Hello $extra'),
        ),
      ),
    );
  }
}

//--------------------------------------------------------------------------------------------------
class SettingsPageParams {
  const SettingsPageParams(this.message);

  final String message;
}
```

</details>


### Screenshots or Videos

<details open>
<summary>Screenshots / Video demonstration</summary>

Class as extra.
https://github.com/flutter/flutter/assets/148017560/2861ba03-2822-4faf-97f6-2d08286deb4a

String as extra.
https://github.com/flutter/flutter/assets/148017560/7535ebaf-1a19-4c80-a41d-a148709c67c2

</details>


### Logs

<details open><summary>Logs</summary>

```console
[Paste your logs here]
```

</details>


### Flutter Doctor output

<details open><summary>Doctor output</summary>

```console
[✓] Flutter (Channel stable, 3.19.3, on macOS 14.4 23E214 darwin-arm64, locale en-PH)
    • Flutter version 3.19.3 on channel stable at /Users/rickimaru/Documents/GitHub/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision ba39319843 (13 days ago), 2024-03-07 15:22:21 -0600
    • Engine revision 2e4ba9c6fb
    • Dart version 3.3.1
    • DevTools version 2.31.1

[✓] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
    • Android SDK at /Users/rickimaru/Library/Android/sdk
    • Platform android-34, build-tools 34.0.0
    • Java binary at: /Applications/Android Studio.app/Contents/jbr/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 17.0.6+0-17.0.6b829.9-10027231)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 15.3)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Build 15E204a
    • CocoaPods version 1.13.0

[✓] Chrome - develop for the web
    • CHROME_EXECUTABLE = /Applications/Brave Browser.app/Contents/MacOS/Brave Browser

[✓] Android Studio (version 2022.3)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 17.0.6+0-17.0.6b829.9-10027231)

[✓] VS Code (version 1.87.2)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.84.0

[✓] Connected device (2 available)
    • macOS (desktop) • macos  • darwin-arm64   • macOS 14.4 23E214 darwin-arm64
    • Chrome (web)    • chrome • web-javascript • Brave Browser 123.1.64.109

[✓] Network resources
    • All expected network resources are available.

• No issues found!
```

</details>