Spring MockMvc doesnt work for my FileModel

I am trying to apply unit test for my image upload operation but when i try to run test MultipartFile doesnt inject MultipartFile of ImageFileModel on the controller.

this is my ImageFileModel :

public class ImageFileModel {

    private Long id;
    private MultipartFile file;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public MultipartFile getFile() {
        return file;
    }

    public void setFile(MultipartFile file) {
        this.file = file;
    }

}

This is My ImageController class :

@Controller
public class ImageController {

    private final ImageService imageService;


    public ImageController(ImageService imageService) {
        this.imageService = imageService;

    }


    @PostMapping("motorcycle/{id}/image")
    public String handleImagePost(@PathVariable String id, @ModelAttribute ImageFileModel fileModel, BindingResult bindingResult){

        new ImageValidator().validate(fileModel,bindingResult);

        if(bindingResult.hasErrors()){
            System.out.println("DEBUG INFO ::::::::::::::: inside error condition for this id : " + id);
            return "motorcycle/imageuploadform";
        }

        imageService.saveImageFile(Long.valueOf(id),fileModel.getFile());

        return "redirect:/motorcycle/" + id + "/show/";

    }

}

This is my ImageControllerTest class :

public class ImageControllerTest {

    @Mock
    ImageService imageService;

    @Mock
    MotorcycleService motorcycleService;

    ImageController controller;

    MockMvc mockMvc;

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

        controller = new ImageController(imageService,motorcycleService);
        mockMvc = MockMvcBuilders.standaloneSetup(controller)
                .setControllerAdvice(new ControllerExceptionHandler())
                .build();
    }

    @Test
    public void handleImagePost() throws Exception {
        //GIVEN
        MockMultipartFile multipartFile =
                new MockMultipartFile("imagefile", "image.jpg", "text/plain",
                        "image byte data..".getBytes());


        //WHEN & THEN
        mockMvc.perform(MockMvcRequestBuilders.fileUpload("/motorcycle/1/image")
                .file(multipartFile)
                .param("id", "2"))

                .andExpect(status().is3xxRedirection())
                .andExpect(header().string("Location", "/motorcycle/1/show/"));

        verify(imageService, times(1)).saveImageFile(anyLong(), any());
    }

}

the error i am getting is :

java.lang.NullPointerException: null
    at com.sam.springbootimagecrudexample.validator.ImageValidator.validate(ImageValidator.java:21)
    at com.sam.springbootimagecrudexample.controller.ImageController.handleImagePost(ImageController.java:74)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:209)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:871)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:777)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:991)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:978)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:881)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:661)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:855)
    at org.springframework.test.web.servlet.TestDispatcherServlet.service(TestDispatcherServlet.java:66)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
    at org.springframework.mock.web.MockFilterChain$ServletFilterProxy.doFilter(MockFilterChain.java:166)
    at org.springframework.mock.web.MockFilterChain.doFilter(MockFilterChain.java:133)
    at org.springframework.test.web.servlet.MockMvc.perform(MockMvc.java:166)
    at com.sam.springbootimagecrudexample.controller.ImageControllerTest.handleImagePost(ImageControllerTest.java:117)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    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.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:538)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:760)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:460)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:206)

I ran my test on debug mode then I saw id value inside ImageFileModel passed on the controller but the file(MultiPartFile) didnt pass. How can I solve this problem?