Internal: Fix faulty getMdiIcon() call

public/main/inc/lib/course_category.lib.php

@@ -384,7 +384,7 @@ class CourseCategory
             $mainUrl = api_get_path(WEB_CODE_PATH).'admin/course_category.php?category='.$categoryCode;
 
             $editIcon = Display::getMdiIcon(ActionIcon::EDIT, 'ch-tool-icon', null, ICON_SIZE_SMALL, get_lang('Edit'));
-            $exportIcon = Display::getMdiIcon(ActionIcon::EXPORT_CSV, 'ch-tool-icon', null, ICON_SIZE_SMALL, get_lang('ExportAsCSV'), '');
+            $exportIcon = Display::getMdiIcon(ActionIcon::EXPORT_CSV, 'ch-tool-icon', null, ICON_SIZE_SMALL, get_lang('ExportAsCSV'));
             $deleteIcon = Display::getMdiIcon(ActionIcon::DELETE, 'ch-tool-icon', null, ICON_SIZE_SMALL, get_lang('Delete'));
             $moveIcon = Display::getMdiIcon(ActionIcon::UP, 'ch-tool-icon', null, ICON_SIZE_SMALL, get_lang('Up in same level'));