remove undefined from outline data source

src/vs/workbench/contrib/codeEditor/browser/outline/documentSymbolsOutline.ts

@@ -142,7 +142,7 @@ class DocumentSymbolsOutline implements IOutline<DocumentSymbolItem> {
 		this._breadcrumbsDataSource = new DocumentSymbolBreadcrumbsSource(_editor, textResourceConfigurationService);
 		const delegate = new DocumentSymbolVirtualDelegate();
 		const renderers = [new DocumentSymbolGroupRenderer(), instantiationService.createInstance(DocumentSymbolRenderer, true)];
-		const treeDataSource: IDataSource<this | undefined, DocumentSymbolItem> = {
+		const treeDataSource: IDataSource<this, DocumentSymbolItem> = {
 			getChildren: (parent) => {
 				if (parent instanceof OutlineElement || parent instanceof OutlineGroup) {
 					return parent.children.values();

src/vs/workbench/contrib/notebook/browser/contrib/outline/notebookOutline.ts

@@ -322,7 +322,7 @@ class NotebookCellOutline implements IOutline<OutlineEntry> {
 			keyboardNavigationLabelProvider: new NotebookNavigationLabelProvider()
 		};
 
-		const treeDataSource: IDataSource<this | undefined, OutlineEntry> = { getChildren: parent => parent instanceof NotebookCellOutline ? this._entries : parent?.children ?? [] };
+		const treeDataSource: IDataSource<this, OutlineEntry> = { getChildren: parent => parent instanceof NotebookCellOutline ? this._entries : parent.children };
 		const delegate = new NotebookOutlineVirtualDelegate();
 		const renderers = [instantiationService.createInstance(NotebookOutlineRenderer)];
 		const comparator = new NotebookComparator();

src/vs/workbench/services/outline/browser/outline.ts

@@ -59,7 +59,7 @@ export interface IQuickPickDataSource<E> {
 
 export interface IOutlineListConfig<E> {
 	readonly breadcrumbsDataSource: IBreadcrumbsDataSource<E>;
-	readonly treeDataSource: IDataSource<IOutline<E> | undefined, E>;
+	readonly treeDataSource: IDataSource<IOutline<E>, E>;
 	readonly delegate: IListVirtualDelegate<E>;
 	readonly renderers: ITreeRenderer<E, FuzzyScore, any>[];
 	readonly comparator: IOutlineComparator<E>;