refactor: consistency for unitialised property

Co-authored-by: Ryan Weaver <[email protected]>

Author: AlexandreGerault

src/React/Resources/assets/src/render_controller.ts

@@ -14,7 +14,7 @@ import { createRoot } from 'react-dom/client';
 import { Controller } from '@hotwired/stimulus';
 
 export default class extends Controller {
-    readonly componentValue: string | undefined;
+    readonly componentValue?: string;
     readonly propsValue?: object;
 
     static values = {