Handle the new undefined logic in TypeScript 4.4

src/languageFeatures.ts

@@ -893,9 +893,10 @@ export class OutlineAdapter extends Adapter implements languages.DocumentSymbolP
 				range: this._textSpanToRange(model, item.spans[0]),
 				selectionRange: this._textSpanToRange(model, item.spans[0]),
 				tags: [],
-				containerName: containerLabel
 			};
 
+			if (containerLabel) result.containerName = containerLabel;
+
 			if (item.childItems && item.childItems.length > 0) {
 				for (let child of item.childItems) {
 					convert(bucket, child, result.name);