public static UserModel toModel(final User user) {
   if (user == null) return null;
   UserModel userModel = new UserModel();
   userModel.setUsername(user.getUsername());
   userModel.setUuid(user.getUuid());
   return userModel;
 }
 public static void mergeModel(final UserModel model, User user) {
   user.setUsername(model.getUsername());
 }