public void validatePack(String pack) {
   if (!SubscriptionPack.isValid(pack)) {
     errors.add("Invalid subscription pack %s", pack);
   }
 }
 public void validatePack(SubscriptionPack pack) {
   if (!SubscriptionPack.isValid(pack.name())) {
     errors.add("Invalid subscription pack %s", pack.name());
   }
 }