fix: type mismatches and handle nullable values

src/Controller/Admin/Teamer/MailingController.php

@@ -2,6 +2,7 @@
 
 namespace App\Controller\Admin\Teamer;
 
+use App\Controller\Traits\AuthenticatedUserTrait;
 use App\Controller\Traits\ReturnUrlTrait;
 use App\Email\MailBodyRenderer;
 use App\Form\TeamerMailingType;
@@ -21,6 +22,7 @@ use Symfony\Component\Security\Http\Attribute\IsGranted;
 
 class MailingController extends AbstractController
 {
+    use AuthenticatedUserTrait;
     use ReturnUrlTrait;
 
     public function __construct(
@@ -47,7 +49,7 @@ class MailingController extends AbstractController
         }
 
         if ($form->isSubmitted() && $form->isValid()) {
-            $this->mailingService->sendPreview($form->getData(), $this->getUser());
+            $this->mailingService->sendPreview($form->getData(), $this->getAuthenticatedUser());
 
             $this->addFlash('success', sprintf(
                 'Die Vorschau wurde an %s gesendet',
@@ -164,7 +166,7 @@ class MailingController extends AbstractController
      */
     private function renderPreview(TeamerMailingDto $mailingDto): array
     {
-        $values = $this->mailingService->placeholderValuesForUser($this->getUser());
+        $values = $this->mailingService->placeholderValuesForUser($this->getAuthenticatedUser());
 
         return [
             'subject' => $this->mailingService->render($mailingDto->getSubject(), $values),