Physical Back button closes the application

**Describe the bug**
Using the physical back button it closes the application instead of going back to the previous screen.

**To Reproduce**
Steps to reproduce the behavior:
1. Follow the flutter_bloc tutorial for firebase login
2. Create a nested router instead to go to HomePage
3. Go to whatever page you want and press back
4. See error

**Expected behavior**
It should go back to the previous page

**Screenshots**

**Logs **
```
[√] Flutter (Channel stable, 2.10.0, on Microsoft Windows [Versione 10.0.19044.1466], locale it-IT)
• Flutter version 2.10.0 at F:\Flutter\flutter
• Upstream repository https://github.com/flutter/flutter.git
• Framework revision 5f105a6ca7 (2 weeks ago), 2022-02-01 14:15:42 -0800
• Engine revision 776efd2034
• Dart version 2.16.0
• DevTools version 2.9.2

[√] Android toolchain - develop for Android devices (Android SDK version 32.1.0-rc1)
• Android SDK at C:\Users\vallo\AppData\Local\Android\sdk
• Platform android-32, build-tools 32.1.0-rc1
• Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
• Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7249189)
• All Android licenses accepted.

[X] Chrome - develop for the web (Cannot find Chrome executable at .\Google\Chrome\Application\chrome.exe)
! Cannot find Chrome. Try setting CHROME_EXECUTABLE to a Chrome executable.

[√] Visual Studio - develop for Windows (Visual Studio Build Tools 2019 16.11.8)
• Visual Studio at C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools
• Visual Studio Build Tools 2019 version 16.11.32002.261
• Windows 10 SDK version 10.0.19041.0

[√] Android Studio (version 2020.3)
• Android Studio at C:\Program Files\Android\Android Studio
• 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 11.0.10+0-b96-7249189)

[√] Connected device (3 available)
• Android SDK built for x86 (mobile) • emulator-5554 • android-x86 • Android 11 (API 30) (emulator)
• Windows (desktop) • windows • windows-x64 • Microsoft Windows [Versione 10.0.19044.1466]
• Edge (web) • edge • web-javascript • Microsoft Edge 97.0.1072.76

[√] HTTP Host Availability
• All required HTTP hosts are available
```