fixes #85039

src/vs/base/browser/dom.ts

@@ -1079,6 +1079,11 @@ function _$<T extends Element>(namespace: Namespace, description: string, attrs?
 
 	Object.keys(attrs).forEach(name => {
 		const value = attrs![name];
+
+		if (typeof value === 'undefined') {
+			return;
+		}
+
 		if (/^on\w+$/.test(name)) {
 			(<any>result)[name] = value;
 		} else if (name === 'selected') {