Unit Tesing - Mockito MyBatis throwing nullpointer exception for selectone returning boolean

I'm using InjectMocks for DAo class and setting dependency using @Mock. The @Before and @After annotations used for setup method and called MockitoAnnotations.initMocks(this);. Here is my mockito code

    @Test
public void testIsMemberExists_DateOffsetFlag_False_Success() {
    //Set Up
    BaseRequest request = new BaseRequest();
    request.setMemberId(11111111L);

    //Expectation
    when(wellnessProgramsDAO.isMemberExists(request)).thenReturn(true);

    //SUT
    boolean response = wellnessProgramsDAO.isMemberExists(request);

    //Verify
    Assert.assertEquals(response, true);
}

Here is method from DAO

    @Override
public boolean isMemberExists(BaseRequest request) {
    LOGGER.debug("Calling DOA impl to get isMemberExists");
    HashMap<String, Object> params = new HashMap<String, Object>();
    params.put("memberId", request.getMemberId());
    if(dateUtil.isDateOffsetFlag()) {
        Date date = referenceDataDAO.getClaimProcessDate();
        params.put(CURRENT_DATE, dateUtil.getCurrentSystemDateInDBFormat(date));
    } else {
        params.put(CURRENT_DATE, dateUtil.getCurrentSystemDateInDBFormat());
    }
    boolean isMemberVIP = getSqlSession().selectOne("wellnessPrograms.isMemberExists", params);
    LOGGER.debug("isMemberExists from DB "+isMemberVIP);
    return isMemberVIP;
}

I'm getting null pointer exception while executing selectone. I have debugged code and session is available, not sure why I'm getting null pointer. Appreciate any help.