/**
  * Sets or gets the coupon model that is processed in the current
  * registration form.
  *
  * @since  1.0.0
  * @param  MS_Addon_Coupon_Model $new_value
  * @return MS_Addon_Coupon_Model
  */
 private static function the_coupon($new_value = null)
 {
     if ($new_value !== null) {
         self::$the_coupon = $new_value;
     } else {
         if (null === self::$the_coupon) {
             self::$the_coupon = MS_Factory::load('MS_Addon_Coupon_Model');
         }
     }
     return self::$the_coupon;
 }