diff --git a/public/main/inc/lib/course.lib.php b/public/main/inc/lib/course.lib.php
index 18c9d578a9..6c867e27fa 100644
--- a/public/main/inc/lib/course.lib.php
+++ b/public/main/inc/lib/course.lib.php
@@ -2571,7 +2571,7 @@ class CourseManager
             $groupCategories = GroupManager::get_categories($course['code']);
             if (!empty($groupCategories)) {
                 foreach ($groupCategories as $category) {
-                    GroupManager::delete_category($category['id'], $course['code']);
+                    GroupManager::delete_category($category['iid'], $course['code']);
                 }
             }
 
diff --git a/public/main/inc/lib/groupmanager.lib.php b/public/main/inc/lib/groupmanager.lib.php
index 6df81bf70c..7029c6dc75 100644
--- a/public/main/inc/lib/groupmanager.lib.php
+++ b/public/main/inc/lib/groupmanager.lib.php
@@ -906,7 +906,7 @@ class GroupManager
 
         $table_group = Database::get_course_table(TABLE_GROUP);
         $table_group_cat = Database::get_course_table(TABLE_GROUP_CATEGORY);
-        $cat_id = intval($cat_id);
+        $cat_id = (int) $cat_id;
         $sql = "SELECT iid FROM $table_group
                 WHERE c_id = $course_id AND category_id='".$cat_id."'";
         $res = Database::query($sql);
@@ -922,7 +922,7 @@ class GroupManager
             }
         }
         $sql = "DELETE FROM $table_group_cat
-                WHERE c_id = $course_id  AND id='".$cat_id."'";
+                WHERE c_id = $course_id  AND iid='".$cat_id."'";
         Database::query($sql);
 
         return true;
diff --git a/src/CoreBundle/EventListener/CourseListener.php b/src/CoreBundle/EventListener/CourseListener.php
index 823662704c..1126fcc811 100644
--- a/src/CoreBundle/EventListener/CourseListener.php
+++ b/src/CoreBundle/EventListener/CourseListener.php
@@ -84,6 +84,10 @@ class CourseListener
                 $em = $container->get('doctrine')->getManager();
                 $course = $em->getRepository(Course::class)->find($courseId);
 
+                if (null === $course) {
+                    throw new NotFoundHttpException($translator->trans('Course does not exist'));
+                }
+
                 //dump("Course loaded from DB $courseId");
                 $courseInfo = api_get_course_info($course->getCode());
             }