title: Flutter Web error - The following UnimplementedError was thrown during a scheduler callback
body: <p>I recently tried to build a web version of my flutter app. It is my first time doing so. After many challenges and errors, all solved with various stack posts, this is the current error I am facing:</p>
  <pre><code>Error: ══╡ EXCEPTION CAUGHT BY SCHEDULER LIBRARY ╞══════════════════════
  The following UnimplementedError was thrown during a scheduler
  callback:
  UnimplementedError
  
  When the exception was thrown, this was the stack:
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart 216:49  throw_
  C:/b/s/w/ir/cache/builder/src/out/host_debug/flutter_web_sdk/lib/_engine/engine/html/scene_builder.dart 231:5              pushShaderMask
  packages/flutter/src/rendering/layer.dart 1812:26                                                                          addToScene
  packages/flutter/src/rendering/layer.dart 440:5                                                                            [_addToSceneWithRetainedRendering]
  packages/flutter/src/rendering/layer.dart 1027:14                                                                          addChildrenToScene
  packages/flutter/src/rendering/layer.dart 1013:5                                                                           addToScene
  packages/flutter/src/rendering/layer.dart 440:5                                                                            [_addToSceneWithRetainedRendering]
  packages/flutter/src/rendering/layer.dart 1027:14                                                                          addChildrenToScene
  packages/flutter/src/rendering/layer.dart 1164:5                                                                           addToScene
  packages/flutter/src/rendering/layer.dart 440:5                                                                            [_addToSceneWithRetainedRendering]
  packages/flutter/src/rendering/layer.dart 1027:14                                                                          addChildrenToScene
  packages/flutter/src/rendering/layer.dart 1164:5                                                                           addToScene
  packages/flutter/src/rendering/layer.dart 440:5                                                                            [_addToSceneWithRetainedRendering]
  packages/flutter/src/rendering/layer.dart 1027:14                                                                          addChildrenToScene
  packages/flutter/src/rendering/layer.dart 1999:5                                                                           addToScene
  packages/flutter/src/rendering/layer.dart 440:5                                                                            [_addToSceneWithRetainedRendering]
  packages/flutter/src/rendering/layer.dart 1027:14                                                                          addChildrenToScene
  packages/flutter/src/rendering/layer.dart 1164:5                                                                           addToScene
  packages/flutter/src/rendering/layer.dart 440:5                                                                            [_addToSceneWithRetainedRendering]
  packages/flutter/src/rendering/layer.dart 1027:14                                                                          addChildrenToScene
  packages/flutter/src/rendering/layer.dart 1164:5                                                                           addToScene
  packages/flutter/src/rendering/layer.dart 440:5                                                                            [_addToSceneWithRetainedRendering]
  packages/flutter/src/rendering/layer.dart 1027:14                                                                          addChildrenToScene
  packages/flutter/src/rendering/layer.dart 1609:5                                                                           addToScene
  packages/flutter/src/rendering/layer.dart 765:5                                                                            buildScene
  packages/flutter/src/rendering/view.dart 231:30                                                                            compositeFrame
  packages/flutter/src/rendering/binding.dart 458:18                                                                         drawFrame
  packages/flutter/src/widgets/binding.dart 895:13                                                                           drawFrame
  packages/flutter/src/rendering/binding.dart 320:5                                                                          [_handlePersistentFrameCallback]
  packages/flutter/src/scheduler/binding.dart 1117:15                                                                        [_invokeFrameCallback]
  packages/flutter/src/scheduler/binding.dart 1055:9                                                                         handleDrawFrame
  packages/flutter/src/scheduler/binding.dart 864:7                                                                          &lt;fn&gt;
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/zone.dart 1182:47                                          _rootRun
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/zone.dart 1093:19                                          run
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/zone.dart 997:7                                            runGuarded
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/zone.dart 1037:23                                          &lt;fn&gt;
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/zone.dart 1190:13                                          _rootRun
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/zone.dart 1093:19                                          run
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/zone.dart 1021:23                                          &lt;fn&gt;
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/_internal/js_dev_runtime/private/isolate_helper.dart 48:19       internalCallback
  ═════════════════════════════════════════════════════════════════
  
      at Object.throw_ [as throw] (http://localhost:11342/dart_sdk.js:4348:11)
      at http://localhost:11342/packages/Okuna/pages/auth/create_account/name_step.dart.lib.js:318203:21
      at Generator.next (&lt;anonymous&gt;)
      at runBody (http://localhost:11342/dart_sdk.js:37976:34)
      at Object._async [as async] (http://localhost:11342/dart_sdk.js:38007:7)
      at http://localhost:11342/packages/Okuna/pages/auth/create_account/name_step.dart.lib.js:318201:66
      at Function.reportError (http://localhost:11342/packages/flutter/src/foundation/debug.dart.lib.js:3696:56)
      at binding$5.WidgetsFlutterBinding.new.[_invokeFrameCallback] (http://localhost:11342/packages/flutter/src/scheduler/binding.dart.lib.js:771:35)
      at binding$5.WidgetsFlutterBinding.new.handleDrawFrame (http://localhost:11342/packages/flutter/src/scheduler/binding.dart.lib.js:734:37)
      at http://localhost:11342/packages/flutter/src/scheduler/binding.dart.lib.js:648:14
      at _rootRun (http://localhost:11342/dart_sdk.js:38250:45)
      at async._CustomZone.new.run (http://localhost:11342/dart_sdk.js:37426:14)
      at async._CustomZone.new.runGuarded (http://localhost:11342/dart_sdk.js:37326:14)
      at http://localhost:11342/dart_sdk.js:37380:33
      at _rootRun (http://localhost:11342/dart_sdk.js:38256:14)
      at async._CustomZone.new.run (http://localhost:11342/dart_sdk.js:37426:14)
      at http://localhost:11342/dart_sdk.js:37365:33
      at internalCallback (http://localhost:11342/dart_sdk.js:24100:11)
  Error: ══╡ EXCEPTION CAUGHT BY SERVICES LIBRARY ╞═══════════════════════
  The following MissingPluginException was thrown while activating
  platform stream on channel uni_links/events:
  MissingPluginException(No implementation found for method listen
  on channel uni_links/events)
  
  When the exception was thrown, this was the stack:
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart 216:49  throw_
  packages/flutter/src/services/platform_channel.dart 157:7                                                                  _invokeMethod
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 45:50            &lt;fn&gt;
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/zone.dart 1198:47                                          _rootRunUnary
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/zone.dart 1100:19                                          runUnary
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/future_impl.dart 143:18                                    handleValue
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/future_impl.dart 696:44                                    handleValueCallback
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/future_impl.dart 725:32                                    _propagateToListeners
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/future_impl.dart 529:5                                     [_completeWithValue]
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/future_impl.dart 567:7                                     &lt;fn&gt;
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/zone.dart 1190:13                                          _rootRun
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/zone.dart 1093:19                                          run
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/zone.dart 1021:23                                          callback
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/schedule_microtask.dart 41:11                              _microtaskLoop
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/schedule_microtask.dart 50:5                               _startMicrotaskLoop
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 166:15           &lt;fn&gt;
  ═════════════════════════════════════════════════════════════════
  
      at Object.throw_ [as throw] (http://localhost:11342/dart_sdk.js:4348:11)
      at http://localhost:11342/packages/Okuna/pages/auth/create_account/name_step.dart.lib.js:318203:21
      at Generator.next (&lt;anonymous&gt;)
      at runBody (http://localhost:11342/dart_sdk.js:37976:34)
      at Object._async [as async] (http://localhost:11342/dart_sdk.js:38007:7)
      at http://localhost:11342/packages/Okuna/pages/auth/create_account/name_step.dart.lib.js:318201:66
      at Function.reportError (http://localhost:11342/packages/flutter/src/foundation/debug.dart.lib.js:3696:56)
      at EventChannel.&lt;anonymous&gt; (http://localhost:11342/packages/flutter/src/services/system_channels.dart.lib.js:1153:39)
      at Generator.throw (&lt;anonymous&gt;)
      at http://localhost:11342/dart_sdk.js:37962:38
      at _rootRunBinary (http://localhost:11342/dart_sdk.js:38278:45)
      at async._CustomZone.new.runBinary (http://localhost:11342/dart_sdk.js:37440:14)
      at _FutureListener.thenAwait.handleError (http://localhost:11342/dart_sdk.js:32783:48)
      at handleError (http://localhost:11342/dart_sdk.js:33335:51)
      at Function._propagateToListeners (http://localhost:11342/dart_sdk.js:33361:17)
      at _Future.new.[_completeWithValue] (http://localhost:11342/dart_sdk.js:33199:23)
      at http://localhost:11342/dart_sdk.js:33222:35
      at _rootRun (http://localhost:11342/dart_sdk.js:38256:14)
      at async._CustomZone.new.run (http://localhost:11342/dart_sdk.js:37426:14)
      at async._AsyncCallbackEntry.new.callback (http://localhost:11342/dart_sdk.js:37365:33)
      at Object._microtaskLoop (http://localhost:11342/dart_sdk.js:38071:13)
      at _startMicrotaskLoop (http://localhost:11342/dart_sdk.js:38077:13)
      at http://localhost:11342/dart_sdk.js:33574:9
  Error: Unsupported operation: Platform._operatingSystem
      at Object.throw_ [as throw] (http://localhost:11342/dart_sdk.js:4348:11)
      at Function._operatingSystem (http://localhost:11342/dart_sdk.js:54995:17)
      at Function.get operatingSystem [as operatingSystem] (http://localhost:11342/dart_sdk.js:55041:27)
      at get _operatingSystem (http://localhost:11342/dart_sdk.js:54954:27)
      at Function.desc.get [as _operatingSystem] (http://localhost:11342/dart_sdk.js:4842:17)
      at get isIOS (http://localhost:11342/dart_sdk.js:54978:26)
      at Function.desc.get [as isIOS] (http://localhost:11342/dart_sdk.js:4842:17)
      at flutter_secure_storage.FlutterSecureStorage.new.[_selectOptions] (http://localhost:11342/packages/flutter_secure_storage/flutter_secure_storage.dart.lib.js:133:36)
      at flutter_secure_storage.FlutterSecureStorage.new.delete (http://localhost:11342/packages/flutter_secure_storage/flutter_secure_storage.dart.lib.js:116:187)
      at storage._SecureStore.new.remove (http://localhost:11342/packages/Okuna/services/storage.dart.lib.js:161:33)
      at storage.OBStorage.new.remove (http://localhost:11342/packages/Okuna/services/storage.dart.lib.js:86:25)
      at user$0.UserService.new._removeStoredUserData (http://localhost:11342/packages/Okuna/pages/auth/create_account/name_step.dart.lib.js:311436:28)
      at _removeStoredUserData.next (&lt;anonymous&gt;)
      at runBody (http://localhost:11342/dart_sdk.js:37976:34)
      at Object._async [as async] (http://localhost:11342/dart_sdk.js:38007:7)
      at user$0.UserService.new.[_removeStoredUserData] (http://localhost:11342/packages/Okuna/pages/auth/create_account/name_step.dart.lib.js:311435:20)
      at user$0.UserService.new.logout (http://localhost:11342/packages/Okuna/pages/auth/create_account/name_step.dart.lib.js:309104:44)
      at logout.throw (&lt;anonymous&gt;)
      at http://localhost:11342/dart_sdk.js:37962:38
      at _rootRunBinary (http://localhost:11342/dart_sdk.js:38278:45)
      at async._CustomZone.new.runBinary (http://localhost:11342/dart_sdk.js:37440:14)
      at _FutureListener.thenAwait.handleError (http://localhost:11342/dart_sdk.js:32783:48)
      at handleError (http://localhost:11342/dart_sdk.js:33335:51)
      at Function._propagateToListeners (http://localhost:11342/dart_sdk.js:33361:17)
      at _Future.new.[_completeWithValue] (http://localhost:11342/dart_sdk.js:33199:23)
      at http://localhost:11342/dart_sdk.js:33222:35
      at _rootRun (http://localhost:11342/dart_sdk.js:38256:14)
      at async._CustomZone.new.run (http://localhost:11342/dart_sdk.js:37426:14)
      at async._AsyncCallbackEntry.new.callback (http://localhost:11342/dart_sdk.js:37365:33)
      at Object._microtaskLoop (http://localhost:11342/dart_sdk.js:38071:13)
      at _startMicrotaskLoop (http://localhost:11342/dart_sdk.js:38077:13)
      at http://localhost:11342/dart_sdk.js:33574:9
  Error: ══╡ EXCEPTION CAUGHT BY SCHEDULER LIBRARY ╞══════════════════════
  The following UnimplementedError was thrown during a scheduler
  callback:
  UnimplementedError
  
  When the exception was thrown, this was the stack:
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart 216:49  throw_
  C:/b/s/w/ir/cache/builder/src/out/host_debug/flutter_web_sdk/lib/_engine/engine/html/scene_builder.dart 231:5              pushShaderMask
  packages/flutter/src/rendering/layer.dart 1812:26                                                                          addToScene
  packages/flutter/src/rendering/layer.dart 440:5                                                                            [_addToSceneWithRetainedRendering]
  packages/flutter/src/rendering/layer.dart 1027:14                                                                          addChildrenToScene
  packages/flutter/src/rendering/layer.dart 1013:5                                                                           addToScene
  packages/flutter/src/rendering/layer.dart 440:5                                                                            [_addToSceneWithRetainedRendering]
  packages/flutter/src/rendering/layer.dart 1027:14                                                                          addChildrenToScene
  packages/flutter/src/rendering/layer.dart 1164:5                                                                           addToScene
  packages/flutter/src/rendering/layer.dart 440:5                                                                            [_addToSceneWithRetainedRendering]
  packages/flutter/src/rendering/layer.dart 1027:14                                                                          addChildrenToScene
  packages/flutter/src/rendering/layer.dart 1164:5                                                                           addToScene
  packages/flutter/src/rendering/layer.dart 440:5                                                                            [_addToSceneWithRetainedRendering]
  packages/flutter/src/rendering/layer.dart 1027:14                                                                          addChildrenToScene
  packages/flutter/src/rendering/layer.dart 1999:5                                                                           addToScene
  packages/flutter/src/rendering/layer.dart 440:5                                                                            [_addToSceneWithRetainedRendering]
  packages/flutter/src/rendering/layer.dart 1027:14                                                                          addChildrenToScene
  packages/flutter/src/rendering/layer.dart 1164:5                                                                           addToScene
  packages/flutter/src/rendering/layer.dart 440:5                                                                            [_addToSceneWithRetainedRendering]
  packages/flutter/src/rendering/layer.dart 1027:14                                                                          addChildrenToScene
  packages/flutter/src/rendering/layer.dart 1164:5                                                                           addToScene
  packages/flutter/src/rendering/layer.dart 440:5                                                                            [_addToSceneWithRetainedRendering]
  packages/flutter/src/rendering/layer.dart 1027:14                                                                          addChildrenToScene
  packages/flutter/src/rendering/layer.dart 1609:5                                                                           addToScene
  packages/flutter/src/rendering/layer.dart 765:5                                                                            buildScene
  packages/flutter/src/rendering/view.dart 231:30                                                                            compositeFrame
  packages/flutter/src/rendering/binding.dart 458:18                                                                         drawFrame
  packages/flutter/src/widgets/binding.dart 895:13                                                                           drawFrame
  packages/flutter/src/rendering/binding.dart 320:5                                                                          [_handlePersistentFrameCallback]
  packages/flutter/src/scheduler/binding.dart 1117:15                                                                        [_invokeFrameCallback]
  packages/flutter/src/scheduler/binding.dart 1055:9                                                                         handleDrawFrame
  packages/flutter/src/scheduler/binding.dart 971:5                                                                          [_handleDrawFrame]
  C:/b/s/w/ir/cache/builder/src/out/host_debug/flutter_web_sdk/lib/_engine/engine/platform_dispatcher.dart 892:13            invoke
  C:/b/s/w/ir/cache/builder/src/out/host_debug/flutter_web_sdk/lib/_engine/engine/platform_dispatcher.dart 145:5             invokeOnDrawFrame
  C:/b/s/w/ir/cache/builder/src/out/host_debug/flutter_web_sdk/lib/_engine/engine.dart 240:45                                &lt;fn&gt;
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/zone.dart 1206:13                                          _rootRunUnary
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/zone.dart 1100:19                                          runUnary
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/zone.dart 1005:7                                           runUnaryGuarded
  C:/b/s/w/ir/cache/builder/src/out/host_debug/dart-sdk/lib/async/zone.dart 1042:26                                          &lt;fn&gt;
  ═════════════════════════════════════════════════════════════════
  
      at Object.throw_ [as throw] (http://localhost:11342/dart_sdk.js:4348:11)
      at http://localhost:11342/packages/Okuna/pages/auth/create_account/name_step.dart.lib.js:318203:21
      at Generator.next (&lt;anonymous&gt;)
      at runBody (http://localhost:11342/dart_sdk.js:37976:34)
      at Object._async [as async] (http://localhost:11342/dart_sdk.js:38007:7)
      at http://localhost:11342/packages/Okuna/pages/auth/create_account/name_step.dart.lib.js:318201:66
      at Function.reportError (http://localhost:11342/packages/flutter/src/foundation/debug.dart.lib.js:3696:56)
      at binding$5.WidgetsFlutterBinding.new.[_invokeFrameCallback] (http://localhost:11342/packages/flutter/src/scheduler/binding.dart.lib.js:771:35)
      at binding$5.WidgetsFlutterBinding.new.handleDrawFrame (http://localhost:11342/packages/flutter/src/scheduler/binding.dart.lib.js:734:37)
      at binding$5.WidgetsFlutterBinding.new.[_handleDrawFrame] (http://localhost:11342/packages/flutter/src/scheduler/binding.dart.lib.js:689:12)
      at Object.invoke (http://localhost:11342/dart_sdk.js:178014:7)
      at _engine.EnginePlatformDispatcher.__.invokeOnDrawFrame (http://localhost:11342/dart_sdk.js:160786:15)
      at http://localhost:11342/dart_sdk.js:175633:55
      at _rootRunUnary (http://localhost:11342/dart_sdk.js:38270:14)
      at async._CustomZone.new.runUnary (http://localhost:11342/dart_sdk.js:37433:14)
      at async._CustomZone.new.runUnaryGuarded (http://localhost:11342/dart_sdk.js:37339:14)
      at http://localhost:11342/dart_sdk.js:37385:34
  Error: MissingPluginException(No implementation found for method findProxy on channel social.okuna/proxy_settings)
      at Object.throw_ [as throw] (http://localhost:11342/dart_sdk.js:4348:11)
      at MethodChannel._invokeMethod (http://localhost:11342/packages/flutter/src/services/system_channels.dart.lib.js:943:21)
      at _invokeMethod.next (&lt;anonymous&gt;)
      at http://localhost:11342/dart_sdk.js:37956:33
      at _rootRunUnary (http://localhost:11342/dart_sdk.js:38264:45)
      at async._CustomZone.new.runUnary (http://localhost:11342/dart_sdk.js:37433:14)
      at _FutureListener.thenAwait.handleValue (http://localhost:11342/dart_sdk.js:32771:29)
      at handleValueCallback (http://localhost:11342/dart_sdk.js:33319:49)
      at Function._propagateToListeners (http://localhost:11342/dart_sdk.js:33357:17)
      at _Future.new.[_completeWithValue] (http://localhost:11342/dart_sdk.js:33199:23)
      at http://localhost:11342/dart_sdk.js:33222:35
      at _rootRun (http://localhost:11342/dart_sdk.js:38256:14)
      at async._CustomZone.new.run (http://localhost:11342/dart_sdk.js:37426:14)
      at async._AsyncCallbackEntry.new.callback (http://localhost:11342/dart_sdk.js:37365:33)
      at Object._microtaskLoop (http://localhost:11342/dart_sdk.js:38071:13)
      at _startMicrotaskLoop (http://localhost:11342/dart_sdk.js:38077:13)
      at http://localhost:11342/dart_sdk.js:33574:9
  </code></pre>
  <p>I have no idea if these are related errors or 4-5 different errors. I can't seem to find the source of where the error is occuring, in which file in my project. Is there a good way to track the error ?</p>
  <p>I seem to have taken all the steps for setting up flutter web. Tried both beta and dev channel.</p>