[Webkit-unassigned] [Bug 224651] New: Web Inspector: Uncaught Exception: null is not an object (evaluating 'this._listeners.get')

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=224651

            Bug ID: 224651
           Summary: Web Inspector: Uncaught Exception: null is not an
                    object (evaluating 'this._listeners.get')
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: All
               URL: http://acko.net/
                OS: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Web Inspector
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: drousso at apple.com
                CC: inspector-bugzilla-changes at group.apple.com

# STEPS TO REPRODUCE
1. inspect <http://acko.net>
2. take a single-frame canvas recording

Uncaught Exceptions:
-----------------------
 - null is not an object (evaluating 'this._listeners.get') (at Object.js:83:52)
    removeEventListener @ Object.js:83:52
    ondetach @ ShaderProgramTreeElement.js:66:55
    _detach @ TreeElement.js:294:26
    removeChildren @ TreeOutline.js:382:26
    removeChildren @ FolderizedTreeElement.js:74:29
    onpopulate @ CanvasTreeElement.js:75:28
    expand @ TreeElement.js:412:28
    reveal @ TreeElement.js:488:39
    revealAndSelect @ TreeElement.js:551:20
    _revealAndSelectRepresentedObject @ ContentBrowserTabContentView.js:307:40
    _contentBrowserCurrentContentViewDidChange @ ContentBrowserTabContentView.js:289:47
    dispatch @ Object.js:129:35
    dispatchEventToListeners @ Object.js:137:17
    _currentContentViewDidChange @ ContentBrowser.js:540:38
    dispatch @ Object.js:129:35
    dispatchEventToListeners @ Object.js:137:17
    showBackForwardEntryForIndex @ ContentViewContainer.js:164:38
    showContentView @ ContentViewContainer.js:141:42
    showRepresentedObject @ ContentBrowserTabContentView.js:218:64
    showRepresentedObject @ GraphicsTabContentView.js:108:36
    _addRecording @ GraphicsTabContentView.js:262:39
    _handleRecordingSavedOrStopped @ GraphicsTabContentView.js:309:27
    dispatch @ Object.js:129:35
    dispatchEventToListeners @ Object.js:145:21
    recordingFinished @ Canvas.js:427:38
    recordingFinished @ CanvasManager.js:232:33
    recordingFinished @ CanvasObserver.js:62:43
    _dispatchEvent @ Connection.js:210:26
    dispatch @ Connection.js:79:32
    dispatchMessageFromTarget @ TargetManager.js:176:39
    dispatchMessageFromTarget @ TargetObserver.js:47:51
    _dispatchEvent @ Connection.js:210:26
    dispatch @ Connection.js:79:32
    dispatch @ InspectorBackend.js:232:52
    ? @ MessageDispatcher.js:42:34

Additional Details:
    cause --> An uncaught exception was thrown while handling event: Canvas.recordingFinished
-----------------------

Notes:
Inspected URL:        http://acko.net/
Loading completed:    true
Frontend User Agent:  Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko)
Dispatch Source:      Protocol Event

Protocol Event:
{"method":"Canvas.recordingFinished","params":{"canvasId":"canvas:0.6","recording":{"version":1,"type":"canvas-webgl","initialState":{"attributes":{"width":1068,"height":1228},"parameters":[{"alpha":false,"depth":true,"stencil":false,"antialias":true,"premultipliedAlpha":true,"preserveDrawingBuffer":false,"failIfMajorPerformanceCaveat":false}],"content":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAABCwAAATMCAYAAABMVhYSAAAAAXNSR0IArs4c6QAAAERlWElmTU0AKgAAAAgAAYdpAAQAAAABAAAAGgAAAAAAA6ABAAMAAAABA…

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