title: Flutter auto_route_generator not building, FormatException: Not an instance of List
body: <p>I'm trying to run Flutter pub run build_runner build,
  to generate a router.g.dart file for navigation.</p>
  <p>I've run a build_runner clean, a whole project clean then build but no luck.
  Im following a tutorial, he just seems to run it exactly with the code I have and its fine. No one else in the comments seem to have this issue and I can't find anything about it online.</p>
  <p>It fails saying:</p>
  <pre><code>[SEVERE] auto_route_generator:autoRouteGenerator on lib/app/router.dart:
  
  FormatException: Not an instance of List.
  [INFO] Running build completed, took 16.2s
  
  [INFO] Caching finalized dependency graph...
  [INFO] Caching finalized dependency graph completed, took 48ms
  
  [SEVERE] Failed after 16.3s
  pub finished with exit code 1
  </code></pre>
  <p>My router.dart code:</p>
  <pre><code>import 'package:auto_route/auto_route_annotations.dart';
  import 'package:stacktest/ui/views/covers/cover_view.dart';
  import 'package:stacktest/ui/views/home/home_view.dart';
  import 'package:stacktest/ui/views/startup/startup_view.dart';
  
  @MaterialAutoRouter()
  class $Router {
    @initial
    StartupView startupViewRoute;
    HomeView homeViewRoute;
    CoverView coverViewRoute;
  }
  </code></pre>
  <p>Pubspec.yaml:</p>
  <pre><code>  sdk: &quot;&gt;=2.7.0 &lt;3.0.0&quot;
  
  dependencies:
    flutter:
      sdk: flutter
  
  
    # The following adds the Cupertino Icons font to your application.
    # Use with the CupertinoIcons class for iOS style icons.
    cupertino_icons: ^0.1.3
    stacked: ^1.7.1+1
    auto_route: 0.6.1
    stacked_services: 0.4.4+3
  
  dev_dependencies:
    build_runner: 1.10.0
    auto_route_generator: 0.6.0
    flutter_test:
      sdk: flutter
  </code></pre>
  <p>Flutter doctor -v</p>
  <pre><code>✓] Flutter (Channel master, 1.20.0-8.0.pre.41, on Mac OS X 10.15.5 19F101, locale en-AU)
      • Flutter version 1.20.0-8.0.pre.41 at /Users/mikaelwills/Documents/Flutter
      • Framework revision fd80503fd3 (34 hours ago), 2020-07-10 14:41:02 +0530
      • Engine revision 9b3e3410f0
      • Dart version 2.9.0 (build 2.9.0-20.0.dev 06cb010247)
  
   
  [✓] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
      • Android SDK at /Users/mikaelwills/Library/Android/sdk
      • Platform android-29, build-tools 29.0.2
      • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
      • Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b49-5587405)
      • All Android licenses accepted.
  
  [✓] Xcode - develop for iOS and macOS (Xcode 11.5)
      • Xcode at /Applications/Xcode.app/Contents/Developer
      • Xcode 11.5, Build version 11E608c
      • CocoaPods version 1.8.4
  
  [✓] Chrome - develop for the web
      • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome
  
  [✓] Android Studio (version 3.5)
      • Android Studio at /Applications/Android Studio.app/Contents
      • Flutter plugin version 42.1.1
      • Dart plugin version 191.8593
      • Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b49-5587405)
  
  [✓] VS Code (version 1.47.0)
      • VS Code at /Applications/Visual Studio Code.app/Contents
      • Flutter extension version 3.12.2
  
  [✓] Connected device (2 available)
      • Web Server (web) • web-server • web-javascript • Flutter Tools
      • Chrome (web)     • chrome     • web-javascript • Google Chrome 83.0.4103.116
  
  • No issues found!
  </code></pre>