NullPointerException in while doing mockito unit test

I am new to mockito Junit testing.This one is my main class which i want to test

package com.ge.health.gam.contactge.util;
import java.io.IOException;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import org.apache.commons.lang.StringUtils;
import org.apache.log4j.Logger;
import org.springframework.stereotype.Component;

@Component
public class IlinqChecksumCalculator {

    private static Logger DATA_LOADER_CHECKSUM_CALCULATOR_LOGGER = Logger.getLogger(IlinqChecksumCalculator.class);

    public String calculateCheckSum(String rfsdata) throws IOException {

        System.out.println(rfsdata);
        String checkSumValue = null;
        if (StringUtils.isNotBlank(rfsdata)) {
            try {
                // Create MessageDigest object for MD5
                MessageDigest digest = MessageDigest.getInstance("MD5");

                // Update input string in message digest
                digest.update(rfsdata.getBytes(), 0, rfsdata.getBytes().length);

                // Converts message digest value in base 16 (hex)
                checkSumValue = new BigInteger(1, digest.digest()).toString(16);

            } catch (NoSuchAlgorithmException exception) {
                DATA_LOADER_CHECKSUM_CALCULATOR_LOGGER.error(
                        "Error in determineInputCheckSum() method during calculation of checksum for Input JSON String for ",
                        exception);
            }
        }
        System.out.println("Final checksum value is:" + checkSumValue);
        return checkSumValue;
    }

}


this one is my test class

package com.ge.health.gam.contactge.util.test;

import static org.junit.Assert.assertEquals;
import static org.mockito.Mockito.when;

import java.io.IOException;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.MockitoAnnotations;
import org.mockito.runners.MockitoJUnitRunner;

import com.ge.health.gam.contactge.util.IlinqChecksumCalculator;

@RunWith(MockitoJUnitRunner.class)
public class IlinqChecksumCalculatorTest {

    private IlinqChecksumCalculator ilinqCheckSum;

    @Before
    public void setUp() throws Throwable {

        MockitoAnnotations.initMocks(this);
    }

    @Test
    public void testCheckSum() throws IOException {

        when(ilinqCheckSum.calculateCheckSum("abcde")).thenReturn("defgh");

        assertEquals("defgh", ilinqCheckSum.calculateCheckSum("abcde"));

    }
}

I am new to mockito Junit testing.This one is my main class which i want to test I am new to mockito Junit testing.This one is my main class which i want to test I am getting null pointer exception...