diff --git a/src/Controller.php b/src/Controller.php
index 34c4aa2..709f880 100644
--- a/src/Controller.php
+++ b/src/Controller.php
@@ -324,7 +324,7 @@ public static function preventClosure(CommonDBTM $item): void
         }
     }
 
-    public static function requireFieldsToClose(CommonITILObject $item): void
+    public static function requireFieldsToClose(CommonDBTM $item): void
     {
         $conf = Config::getConfig();
         if ($conf->fields['is_active'] != 1) {
@@ -336,8 +336,8 @@ public static function requireFieldsToClose(CommonITILObject $item): void
 
         // Determine the configuration suffix and actor classes based on item type
         $configSuffix = '_' . strtolower($itemtype);
-        $userClass = $item->userlinkclass;
-        $groupClass = $item->grouplinkclass;
+        $userClass = $item->userlinkclass ?? '';
+        $groupClass = $item->grouplinkclass ?? '';
         $itemIdField = $item->getForeignKeyField();
 
         // Check for required technician