Method getOwnerName causes call to undefined method "getPersoon".

getOwnerName assumes that every instance of "user_class" has a method named getPersoon. In kinderdagverblijf projecten, user_class is equal to "Persoon" and does not have a method called "getPersoon".

Fix will check if a method called "getPersoon" exists in user_class, if the method does not exist, it will return a string representation of the instance of user_class.

This fix is just as bad as the earlier code because we assume that every user_class has a __toString method defined.