Cannot read properties of null (reading 'getFoldingState')

[Yoyokrazy]

Originally created by @roblourens in https://github.com/microsoft/vscode-copilot/issues/6537

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Filing this in vscode-copilot because I reproed this with the copilot notebook and I don't want to post these steps publicly

• Enable "github.copilot.chat.notebookLogEnabled": true, and

"github.copilot.advanced": {
  "conversationLoggingEnabled": true,

• Run "Show Chat Log Notebook"
• Make a chat request
• Repeat
• Sometimes, see a bunch of errors

The chat notebook makes edits really quickly to the open notebook editor, which is probably an unusual case, but this seems to be causing an issue

2024-06-28 16:20:33.938 [error] Cannot read properties of null (reading 'getFoldingState'): TypeError: Cannot read properties of null (reading 'getFoldingState')
    at get foldingState (vscode-file://vscode-app/Users/roblou/code/vscode/out/vs/workbench/contrib/notebook/browser/viewModel/markupCellViewModel.js:73:41)
    at NotebookOutlineRenderer.setupFolding (vscode-file://vscode-app/Users/roblou/code/vscode/out/vs/workbench/contrib/notebook/browser/contrib/outline/notebookOutline.js:167:97)
    at NotebookOutlineRenderer.renderElement (vscode-file://vscode-app/Users/roblou/code/vscode/out/vs/workbench/contrib/notebook/browser/contrib/outline/notebookOutline.js:142:22)
    at TreeRenderer.renderElement (vscode-file://vscode-app/Users/roblou/code/vscode/out/vs/base/browser/ui/tree/abstractTree.js:294:27)
    at PipelineRenderer.renderElement (vscode-file://vscode-app/Users/roblou/code/vscode/out/vs/base/browser/ui/list/listWidget.js:967:26)
    at ListView.insertItemInDOM (vscode-file://vscode-app/Users/roblou/code/vscode/out/vs/base/browser/ui/list/listView.js:638:23)
    at ListView._splice (vscode-file://vscode-app/Users/roblou/code/vscode/out/vs/base/browser/ui/list/listView.js:430:26)
    at ListView.splice (vscode-file://vscode-app/Users/roblou/code/vscode/out/vs/base/browser/ui/list/listView.js:347:29)
    ...