老师，请问UserManager里面的checkUser返回值为NULL妥否？

public class UserManager {

public String checkUser(User one, User two) {

if (one.getUserName().equals(two.getUserName())&one.getPassWord().equals(two.getPassWord())) {

System.out.println("用户名或密码一致");

}else {

System.out.println("用户名或密码不一致");

}

return null ;

}

}