src/vs/workbench/contrib/notebook/common/notebookEditorModel.ts/SimpleNotebookEditorModel/_isStoredFileWorkingCopy
class SimpleNotebookEditorModel:	private static _isStoredFileWorkingCopy(candidate?: IStoredFileWorkingCopy<NotebookFileWorkingCopyModel> | IUntitledFileWorkingCopy<NotebookFileWorkingCopyModel>): candidate is IStoredFileWorkingCopy<NotebookFileWorkingCopyModel> {
		const isUntitled = candidate && candidate.capabilities & WorkingCopyCapabilities.Untitled;

		return !isUntitled;
	}