Java Spring Reactive Rest API Test Class Gives Error - Null Pointer Exception

I am trying to create a very basic rest API using the Spring Reactive programming and I wanted to also try the testing possibilities with Reactive Stack.

However when I try to test the service implementation, I get a Null pointer error and this happens after I call any kind of action method like: doNext, flatMap, block etc. (in the form of userService.save(user).doNext, userService.save(user).flatMap, userService.save(user).block() and etc.)

You can find the full code and the gradle setup in the following github repository: https://github.com/mesarikaya/restAPI

Your helps would be much appreciated.

Below is the test code if you would like to have a quick look:

@Slf4j
@ExtendWith(MockitoExtension.class)
public class UserServiceTest {

    @Mock
    private UserRepository userRepository;
    private User existingUser;
    private User newUser;
    private User returnUser;
    private Logger logger = LoggerFactory.getLogger(UserServiceTest.class);
    @InjectMocks
    private UserServiceImpl userService;

    @BeforeEach
    public void setUp() {
        System.out.println("@Beforeeach is called!");
        MockitoAnnotations.initMocks(this);

        // Create Existing Account
        existingUser = new User();
        existingUser.setEmail("abc@gmail.com");
        existingUser.setFirstName("First");
        existingUser.setMiddleName("Middle");
        existingUser.setLastName("Last");
        existingUser.setActive(true);
        existingUser.setMobileNumber("021234234");
        existingUser.setVerified(false);
        existingUser.setPermalink("abcgmailcom");

        Address address1 = new Address();
        address1.setStreetName("asda");
        address1.setHouseNumber("asd");
        address1.setCity("asdasd");
        address1.setCountry("asdasd");
        address1.setZipcode("sasd123");
        existingUser.setAddress(address1);

        // New User
        // Create Existing Account
        newUser = new User();
        newUser.setFirstName("NewFirst");
        newUser.setMiddleName("NewMiddle");
        newUser.setLastName("NewLast");
        newUser.setActive(true);
        newUser.setMobileNumber("0123123");
        newUser.setVerified(false);
        newUser.setOauthId("123123123");

        Address address2 = new Address();
        address2.setStreetName("ADress2");
        address2.setHouseNumber("asda");
        address2.setCity("asdsad");
        address2.setCountry("asd");
        address2.setZipcode("asdasd");
        newUser.setAddress(address2);
        // newUser.setId((ObjectId) new ObjectIdGenerator().generate());
        userService.saveOrUpdateUser(existingUser);
        userService.saveOrUpdateUser(newUser);

        System.out.println("Existing user: " + existingUser);
        System.out.println("New User: " + newUser);
    }

    @Test
    public void findUser(){
        User user = userService.saveOrUpdateUser(existingUser).block();
        Mono<User> userMono = userService.saveOrUpdateUser(existingUser);

        StepVerifier
                .create(userMono)
                .assertNext(u -> {
                    assertEquals(existingUser.getEmail(), u.getEmail());
                    assertEquals(existingUser.getLastName() , u.getLastName());
                })
                .expectComplete()
                .verify();

        assertEquals(user.getEmail(), existingUser.getEmail());
        assertEquals(user.getId(), existingUser.getId());
    }
}

Here is the error message:

FYI- Repository is recognized : com.mes.gotogether.repositories.UserRepository$MockitoMock$612061122

java.lang.NullPointerException at com.mes.gotogether.services.UserServiceImpl.saveOrUpdateUser(UserServiceImpl.java:56) at com.mes.gotogether.services.UserServiceTest.setUp(UserServiceTest.java:77) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.base/java.lang.reflect.Method.invoke(Method.java:566) at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:532) at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:115) at org.junit.jupiter.engine.descriptor.ClassTestDescriptor.invokeMethodInExtensionContext(ClassTestDescriptor.java:436) at org.junit.jupiter.engine.descriptor.ClassTestDescriptor.lambda$synthesizeBeforeEachMethodAdapter$14(ClassTestDescriptor.java:424) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeBeforeEachMethods$2(TestMethodTestDescriptor.java:136) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:72) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeBeforeMethodsOrCallbacksUntilExceptionOccurs(TestMethodTestDescriptor.java:156) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeBeforeEachMethods(TestMethodTestDescriptor.java:135) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:110) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:59) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$4(NodeTestTask.java:108) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:72) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:98) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:74) at java.base/java.util.ArrayList.forEach(ArrayList.java:1540) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$4(NodeTestTask.java:112) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:72) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:98) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:74) at java.base/java.util.ArrayList.forEach(ArrayList.java:1540) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$4(NodeTestTask.java:112) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:72) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:98) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:74) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32) at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57) at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:220) at org.junit.platform.launcher.core.DefaultLauncher.lambda$execute$6(DefaultLauncher.java:188) at org.junit.platform.launcher.core.DefaultLauncher.withInterceptedStreams(DefaultLauncher.java:202) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:181) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:128) at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:74) at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47) at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242) at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)