Theme hook not implemented

auction_add_page theme function used in ModelUIController::hook_menu() will not work if called like theme('model_add_page', array('content' => $content)) because the hook theme that defines it is not implemented. It should be just added to model.module:

/**
 * Implements hook_theme().
 */
function model_theme($existing, $type, $theme, $path) {
  return array(
    'model_add_list' => array(
      'variables' => array('content' => NULL),
    ),
  );
}