docs: public void checkUserName(String userName) throws CmsIllegalArgumentException {
  
          if (CmsStringUtil.isEmptyOrWhitespaceOnly(userName)) {
              throw new CmsIllegalArgumentException(
                  Messages.get().container(Messages.ERR_BAD_USERNAME_EMPTY_0, userName));
          }
  
          CmsStringUtil.checkName(userName, USERNAME_CONSTRAINTS, Messages.ERR_BAD_USERNAME_4, Messages.get());
      }