Actual response is returning null in unit test using JUnit 4.12

Question

So, i'm trying to create a unit test since its my first time doing this and here is the code:

package com.convergeict.shoppingcartservice.controller;

import com.convergeict.shoppingcartservice.model.CartDetails.CartSummary;
import com.convergeict.shoppingcartservice.model.CartDetails.ChargeSummary;
import com.convergeict.shoppingcartservice.model.CartDetails.MapOfCartItem;
import com.convergeict.shoppingcartservice.response.GenericResponse;
import com.convergeict.shoppingcartservice.service.CartDetailsService;
import org.junit.Before;
import org.junit.Test;
import org.junit.jupiter.api.BeforeEach;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.MockitoAnnotations;
import org.springframework.http.ResponseEntity;

import java.util.ArrayList;
import java.util.List;

import static org.junit.Assert.*;
import static org.mockito.Mockito.*;

public class CartDetailsControllerTest {

    @InjectMocks
    private CartDetailsController cartDetailsController;

    @Mock
    private CartDetailsService cartDetailsService;

    @Before
    public void setUp() {
        MockitoAnnotations.initMocks(this);
    }

    @Test
    public void testGetCartDetailsSuccess() {
        String cartInstanceIdentifier = "937f4199-ef42-470a-8a35-719c39a3c064";

        CartSummary cartSummary = CartSummary.builder()
                .statusCode("0000")
                .statusDesc("Success")
                .totalChargeSummary(new ChargeSummary())
                .cartItemSummaryList(new ArrayList<>())
                .build();


        ResponseEntity<GenericResponse<?>> actualResponse = cartDetailsController.getCartDetails(cartInstanceIdentifier);
        System.out.println(actualResponse);

        assertNotNull(actualResponse);
    }

}

here is the CartDetailsController class:

@RestController
@RequestMapping("/api")
public class CartDetailsController {

    @Autowired
    private CartDetailsService cartDetailsService;

    @RequestMapping(value = "/v1/cart-details", method = RequestMethod.GET)
    public ResponseEntity<GenericResponse<?>> getCartDetails(@RequestParam String cartInstanceIdentifier) {
        return cartDetailsService.getCartDetails(cartInstanceIdentifier);
    }

}

Upon running the testGetCartDetailsSuccess test, it's throwing me this exception:

java.lang.NullPointerException: Cannot invoke "com.convergeict.shoppingcartservice.service.CartDetailsService.getCartDetails(String)" because "this.cartDetailsService" is null

    at com.convergeict.shoppingcartservice.controller.CartDetailsController.getCartDetails(CartDetailsController.java:21)
    at com.convergeict.shoppingcartservice.controller.CartDetailsControllerTest.testGetCartDetailsSuccess(CartDetailsControllerTest.java:44)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.base/java.lang.reflect.Method.invoke(Unknown Source)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)
    at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)
    at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:232)
    at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:55)

I have exhausted my options and can't seem to debug/fix this properly, I need help thanks.

I was expecting the actual response to return an actual response when hitting the actual API so I can assert it to a not null.