Steps to Reproduce: In User.java, run the function login() and changePwd(), we can see the return results of if conditional sentences. Expected output: When method iUserDAO.queryUser() or iUserDAO.changePwd() is true, it will return a new constructor, otherwise it will return null. Actual output: It only can return new constructor when if conditional sentences are true.
Resolution: We should add a branch to return null in the Login() and changePwd() in the if conditional sentences.