/*
 * Updating the Object works
 */
$m->userdata->update( array("id_user" => (int)$user->getId()),  array('$set' =>   array('mayHaveTriviadoYccount' => 2)));


/*
 * Unsetting does not work
 */
$m->userdata->update( array("id_user" => (int)$user->getId()),  array('$unset' => array('mayHaveTriviadoYccount' => 1)));