If you would call get_courses() with a limited number of fields like 

 $categorycourses = get_courses($categoryid, 'c.sortorder ASC', 'c.id');

you would get following error:

Undefined property: stdClass::$visible

/var/www/project/respect/course/classes/category.php:695
/var/www/project/respect/lib/datalib.php:652