public String newUser(RegisterVO vo) {
    logger.debug("trying to new a user");
    SqlSession sqlSession = MySqlSession.openMasterSession();

    RegisterUser registerUser = null;
    try {
      registerUser =
          sqlSession.selectOne("db.RegisterUserMapper.selectUserByTelNumber", vo.getTelNumber());
    } catch (Exception e) {
      e.printStackTrace();
    }
    logger.debug(registerUser);

    RegisterUser newUser = new RegisterUser();

    newUser.setName(vo.getName());
    newUser.setTelNumber(vo.getTelNumber());
    newUser.setPassword(vo.getPassword());
    newUser.setEmail(vo.getEmail());
    sqlSession.insert("db.RegisterUserMapper.addUser", newUser);

    logger.debug(newUser);
    return newUser.getTelNumber();
  }