adding a check on the variable (#27021)

GitOrigin-RevId: 9ecc517ff9bee1dac14e579d494294c0efeb6b69

services/web/frontend/js/features/navbar/index.ts

@@ -1,6 +1,6 @@
 const toggleButton = document.getElementById('navbar-toggle-btn') as HTMLElement
 
-toggleButton.addEventListener('click', () => {
+toggleButton?.addEventListener('click', () => {
   // Delay allows Bootstrap to update aria-expanded first
   setTimeout(() => {
     const isExpanded = toggleButton.getAttribute('aria-expanded') === 'true'