Written in eclipse, problems after querying the database connection

bosses , Help the kids , One good turn deserves another , A good man lives a long life ！！！！ Just started learning java And the database , I wrote something about this , As a result, my eclipse After connecting to the database , Just started to query , Always report mistakes , The query failed , And the display java.lang.NullPointerException, The code reports an error in the following code （ if (rs.next()) ）, What about this one ？ Here is part of the code :
if (account.length()!=0&&password.length()!=0) {
try { // Both passwords and accounts are valid
//userDao Determine if the password is correct
rs = userDao.selectByAccountAndPassword(account, password） // Correct account password , The returned result set is not null
if (rs.next()) {
user = userDao.saveUser(rs);
if (user.getRole() == BaseDao.userRoLeStudent) {
System.out.println(" It's the students ");