diff --git a/class.ilInteractiveVideoOpenCastGUI.php b/class.ilInteractiveVideoOpenCastGUI.php
index f5ee1b6..e1ad78f 100644
--- a/class.ilInteractiveVideoOpenCastGUI.php
+++ b/class.ilInteractiveVideoOpenCastGUI.php
@@ -270,11 +270,11 @@ public function __construct(ilCtrl $oldIlCtrl)
              */
             public function getLinkTargetByClass(
                 $a_class,
-                $a_cmd = "",
-                $a_anchor = "",
-                $a_asynch = false,
-                $xml_style = true
-            ) {
+                ?string $a_cmd = null,
+                ?string $a_anchor = null,
+                bool $is_asynch = false,
+                bool $has_xml_style = false
+            ): string {
 
                 $this->oldIlCtrl->setParameter(new ilObjInteractiveVideoGUI(), 'xvid_plugin_ctrl', ilInteractiveVideoOpenCastGUI::class);
                 $this->oldIlCtrl->setParameter(new ilObjInteractiveVideoGUI(), 'xvid_source_id', 'opc');
@@ -325,4 +325,4 @@ public function createCtrlFake($dic): void
         $this->ajax_url = $this->ilCtrlFake->getLinkTargetByClass(['ilRepositoryGUI', 'ilObjInteractiveVideoGUI'], 'getAjaxOpenCastTable','', true, false);
 
     }
-}
\ No newline at end of file
+}