Fix #58309 - possibly same as #58311 but be safe

src/vs/workbench/parts/preferences/browser/tocTree.ts

@@ -48,8 +48,10 @@ export class TOCTreeModel {
 	}
 
 	public update(): void {
+		if (this._settingsTreeRoot) {
 			this.updateGroupCount(this._settingsTreeRoot);
 		}
+	}
 
 	private updateGroupCount(group: SettingsTreeGroupElement): void {
 		group.children.forEach(child => {