diff --git a/components/ILIAS/Test/src/Participants/ParticipantTableActions.php b/components/ILIAS/Test/src/Participants/ParticipantTableActions.php
index d639d59b790b..c1dbb4695e4d 100644
--- a/components/ILIAS/Test/src/Participants/ParticipantTableActions.php
+++ b/components/ILIAS/Test/src/Participants/ParticipantTableActions.php
@@ -202,16 +202,20 @@ protected function resolveSelectedParticipants(TableAction $action, array|string
         if ($selected_participants === 'ALL_OBJECTS') {
             return array_filter(
                 iterator_to_array($this->repository->getParticipants($this->test_obj->getTestId())),
-                fn(Participant $participant) => $action->allowActionForRecord($participant)
+                static fn(Participant $participant): bool => $action->allowActionForRecord($participant)
             );
         }
 
+        if (!is_array($selected_participants)) {
+            return [];
+        }
+
         return array_filter(
             array_map(
-                fn(int $user_id) => $this->repository->getParticipantByUserId($this->test_obj->getTestId(), $user_id),
+                fn(int $user_id): ?Participant => $this->repository->getParticipantByUserId($this->test_obj->getTestId(), $user_id),
                 $selected_participants
             ),
-            fn(Participant $participant) => $action->allowActionForRecord($participant)
+            static fn(?Participant $participant): bool => $participant instanceof Participant && $action->allowActionForRecord($participant)
         );
     }
 }