diff --git a/Classes/SelectCategories.php b/Classes/SelectCategories.php
index c24af3f3..186b6aaf 100644
--- a/Classes/SelectCategories.php
+++ b/Classes/SelectCategories.php
@@ -17,6 +17,7 @@
 
 use DirectMailTeam\DirectMail\Repository\TempRepository;
 use TYPO3\CMS\Core\Localization\LanguageService;
+use TYPO3\CMS\Core\Site\Entity\NullSite;
 use TYPO3\CMS\Core\Utility\GeneralUtility;
 
 /**
@@ -39,11 +40,17 @@ public function getLocalizedCategories(array &$params): void
         $lang = $this->getLang();
 
         $site = $params['site'];
-        $languages = $site->getAllLanguages();
-        foreach($languages as $language) {
-            if($language->getLocale()->getLanguageCode() == $lang) {
-                $sysLanguageUid = $language->getLanguageId();
+
+        // Check if the site is not a NullSite before calling getAllLanguages()
+        if (!$site instanceof NullSite) {
+            $languages = $site->getAllLanguages();
+            foreach ($languages as $language) {
+                if ($language->getLocale()->getLanguageCode() == $lang) {
+                    $sysLanguageUid = $language->getLanguageId();
+                }
             }
+        } else {
+            $sysLanguageUid = 0;
         }
 
         if (is_array($params['items']) && !empty($params['items'])) {