Null pointer Exception in Test Cases [duplicate]

This question already has an answer here:

• What is a Null Pointer Exception, and how do I fix it? 12 answers

    public class UserTest {

        private User user;
        private Account account;
        private Customer customer;
        private UserService userService=new UserService();
        private CustomerService customerService=new CustomerService();
        private EmployeeService employeeService=new EmployeeService();
        private SessionFactory sessionFactory;
        private Session session;

        @Before
        public void setUp() throws Exception
        {
            sessionFactory=Mockito.mock(SessionFactory.class);
            session=Mockito.mock(Session.class);

        }

        @Test
        public void shouldNotValidateWrongPassword() 
        {
            String newPassword="xyz";
            user = new Customer(1,"",null,' ',' ',"dgh",' ',"");
            field("sessionFactory").ofType(SessionFactory.class).in(userService).set(sessionFactory);
            Mockito.when(sessionFactory.getCurrentSession()).thenReturn(session);
            Mockito.when(session.get(Customer.class, 1)).thenReturn(user);
                assertNotSame(userService.validate(1, newPassword), false);
        }

        @Test
        public void testgetUser() 
        {
            user = new Customer(1,"",null,' ',' ',"hello",' ',"");
            field("sessionFactory").ofType(SessionFactory.class).in(customerService).set(sessionFactory);
            Mockito.when(sessionFactory.getCurrentSession()).thenReturn(session);


            Mockito.when(session.get(User.class, 1)).thenReturn(user);
                assertNotNull(employeeService.getUser(1));
}

Methods for which I am writing test cases is as follows:

@Transactional
    public boolean validate(int username, String password) {
        User user = getUser(username);

        System.out.println(username + password);

        return user.validate(password);

    }

@Transactional
    public User getUser(int userId) {
        System.out.println("Employee service called!");
        User user = (User) sessionFactory.getCurrentSession().get(User.class, userId);
        return user;
    }

I have these two cases...for which I am getting null pointer Exception.I am very new to write test cases.please anyone help to figure out where it goes wrong?