[Blazor] - Issue calling submitRequest on data-enhanced form

Co-authored-by: Adit Sheth <[email protected]>

Fixes #58244

This PR fixes an issue where calling requestSubmit on a form with the data-enhance attribute caused an uncaught TypeError due to accessing a member on a null event.submitter.

The change replaces the non-null assertion operator (!) with the optional chaining operator (?) to properly handle cases where event.submitter is null.

Author: shethaadit

src/Components/Web.JS/src/Services/NavigationEnhancement.ts

@@ -144,7 +144,7 @@ function onDocumentSubmit(event: SubmitEvent) {
     const formData = new FormData(formElem);
 
     const submitterName = event.submitter?.getAttribute('name');
-    const submitterValue = event.submitter!.getAttribute('value');
+    const submitterValue = event.submitter?.getAttribute('value');
     if (submitterName && submitterValue) {
       formData.append(submitterName, submitterValue);
     }