semantics_helper.dart:124 Uncaught TypeError: Cannot read property 'Symbol(dartx.remove)' of null
    at _engine.DesktopSemanticsEnabler.new.tryEnableSemantics (semantics_helper.dart:124)
    at _engine.SemanticsHelper.new.shouldEnableSemantics (semantics_helper.dart:43)
    at _engine.EngineSemanticsOwner.__.receiveGlobalEvent (semantics.dart:1349)
    at HTMLElement.<anonymous> (pointer_binding.dart:172)
tryEnableSemantics @ semantics_helper.dart:124
shouldEnableSemantics @ semantics_helper.dart:43
receiveGlobalEvent @ semantics.dart:1349
(anonymous) @ pointer_binding.dart:172

C:\Users\john\dev\slider_test>flutter build web --verbose
[  +24 ms] executing: [C:\src\flutter\] git -c log.showSignature=false log -n 1 --pretty=format:%H
[  +68 ms] Exit code 0 from: git -c log.showSignature=false log -n 1 --pretty=format:%H
[        ] e4b809b7c8d90f0b4419290bba163ed0dfcb9475
[        ] executing: [C:\src\flutter\] git describe --match v*.*.* --first-parent --long --tags
[  +79 ms] Exit code 0 from: git describe --match v*.*.* --first-parent --long --tags
[        ] v1.12.15-16-ge4b809b7c
[   +7 ms] executing: [C:\src\flutter\] git rev-parse --abbrev-ref --symbolic @{u}
[  +42 ms] Exit code 0 from: git rev-parse --abbrev-ref --symbolic @{u}
[        ] origin/master
[        ] executing: [C:\src\flutter\] git ls-remote --get-url origin
[  +39 ms] Exit code 0 from: git ls-remote --get-url origin
[   +1 ms] https://github.com/flutter/flutter.git
[  +87 ms] executing: [C:\src\flutter\] git rev-parse --abbrev-ref HEAD
[  +80 ms] Exit code 0 from: git rev-parse --abbrev-ref HEAD
[   +1 ms] master
[  +48 ms] Artifact Instance of 'AndroidMavenArtifacts' is not required, skipping update.
[   +1 ms] Artifact Instance of 'AndroidGenSnapshotArtifacts' is not required, skipping update.
[   +1 ms] Artifact Instance of 'AndroidInternalBuildArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IOSEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterWebSdk' is not required, skipping update.
[   +4 ms] Artifact Instance of 'WindowsEngineArtifacts' is not required, skipping update.
[   +1 ms] Artifact Instance of 'MacOSEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'LinuxEngineArtifacts' is not required, skipping update.
[   +2 ms] Artifact Instance of 'LinuxFuchsiaSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'MacOSFuchsiaSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterRunnerSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterRunnerDebugSymbols' is not required, skipping update.
[  +12 ms] Artifact Instance of 'MaterialFonts' is not required, skipping update.
[   +1 ms] Artifact Instance of 'GradleWrapper' is not required, skipping update.
[   +5 ms] Artifact Instance of 'AndroidMavenArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'AndroidGenSnapshotArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'AndroidInternalBuildArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IOSEngineArtifacts' is not required, skipping update.
[   +2 ms] Artifact Instance of 'FlutterSdk' is not required, skipping update.
[        ] Artifact Instance of 'WindowsEngineArtifacts' is not required, skipping update.
[   +2 ms] Artifact Instance of 'MacOSEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'LinuxEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'LinuxFuchsiaSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'MacOSFuchsiaSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterRunnerSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterRunnerDebugSymbols' is not required, skipping update.
[        ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[   +1 ms] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[   +2 ms] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[ +185 ms] Generating
C:\Users\john\dev\slider_test\android\app\src\main\java\io\flutter\plugins\GeneratedPluginRegistrant.java
[ +120 ms] Generating
C:\Users\john\dev\slider_test\android\app\src\main\java\io\flutter\plugins\GeneratedPluginRegistrant.java
[  +29 ms] Compiling lib\main.dart for the Web...
[  +17 ms] Initializing file store
[  +19 ms] Done initializing file store
[  +82 ms] Skipping target: web_entrypoint
[+1863 ms] Skipping target: dart2js
[  +39 ms] Skipping target: web_release_bundle
[   +3 ms] Persisting file store
[  +16 ms] Done persisting file store
[  +15 ms] Compiling lib\main.dart for the Web... (completed in 2.0s)
[   +2 ms] "flutter web" took 2,585ms.

C:\Users\john\dev\slider_test>flutter analyze
Analyzing slider_test...
No issues found! (ran in 1.8s)

C:\Users\john\dev\slider_test>flutter doctor -v
[√] Flutter (Channel master, v1.12.16-pre.16, on Microsoft Windows [Version 10.0.17763.864], locale en-US)
    • Flutter version 1.12.16-pre.16 at C:\src\flutter
    • Framework revision e4b809b7c8 (40 minutes ago), 2019-11-27 10:18:43 -0800
    • Engine revision fad1b23c42
    • Dart version 2.7.0


[√] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
    • Android SDK at C:\Users\john\AppData\Local\Android\sdk
    • Android NDK location not configured (optional; useful for native profiling support)
    • Platform android-29, build-tools 29.0.2
    • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b03)
    • All Android licenses accepted.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files (x86)\Google\Chrome\Application\chrome.exe

[√] Android Studio (version 3.5)
    • Android Studio at C:\Program Files\Android\Android Studio
    • Flutter plugin version 40.1.2
    • Dart plugin version 191.8423
    • Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b03)

[√] VS Code (version 1.40.2)
    • VS Code at C:\Users\john\AppData\Local\Programs\Microsoft VS Code
    • Flutter extension version 3.6.0

[√] Connected device (2 available)
    • Chrome     • chrome     • web-javascript • Google Chrome 78.0.3904.108
    • Web Server • web-server • web-javascript • Flutter Tools

• No issues found!