diff --git a/lib/classes/MyRealmModel.php b/lib/classes/MyRealmModel.php
index 8fe3fee4d5d1cfef1aa4da66f55152aa1450d946..19474869c47dcfa842bf90509ff6c3607208961c 100644
--- a/lib/classes/MyRealmModel.php
+++ b/lib/classes/MyRealmModel.php
@@ -526,7 +526,7 @@ class MyRealmModel
         $claiming = DBManager::get()->fetchAll($sql, [$user_id]);
         $csets    = [];
         foreach ($claiming as $k => $claim) {
-            if (!$csets[$claim['set_id']]) {
+            if (!isset($csets[$claim['set_id']])) {
                 $csets[$claim['set_id']] = new CourseSet($claim['set_id']);
             }
             $cs = $csets[$claim['set_id']];