Error with JUnit testing failure condition with Custom Exception

I am writing a test case for the Rest Controller for an error condition and when I set expected exception to Exception.class the test runs with no errors. When I change the expected exception to CustomException.class, the test fails with assertion error

Here is my Controller class:

@RestController
public class CustomController<CustomFieldRequest customFieldRequest, CustomField customField> {
    @PutMapping(path = "/{customFieldId}",
            consumes = MediaType.APPLICATION_JSON_VALUE, produces = {MediaType.APPLICATION_JSON_VALUE, MediaType.APPLICATION_ATOM_XML_VALUE})
    public CustomField updateCustomField(@PathVariable String customFieldId, @RequestBody CustomFieldRequest customFieldRequest) throws CustomException {
        customFieldRequest.setAuthorId(getUser());
        customFieldRequest.setId(customFieldId);
        return CustomService.updateCustomeField(customFieldRequest);
    }
}

Here is my service class:

@Service
public class CustomServiceImpl implements CustomService {
    @Override
    public CustomField updateCustomeField(CustomFieldRequest customFieldRequest) throws CustomException {

    }
}

Here is my custom exception class:

public class CustomException extends Exception {
    public CustomException(final String  message) {
        super(message);
    }

    public CustomException(final String  message, final Throwable cause) {
        super(message, cause);
    }
}

Here is my test class:

public class CustomControllerTest {
    private CustomService customService = Mockito.mock(CustomService.class);

    @Test(expected=Exception.class)
    public void updateCustomFieldThrowsException() throws CustomException {
    	//exception.expect(Exception.class);
        CustomFieldRequest request = getRequest();

        when(customService.updateCustomeField(request)).thenThrow(Exception.class);
        //customController.updateCustomField(request.getId(), request);
    }
}

As mentioned above if I change my expected exception to CustomException.class in the test like below:

    @Test(expected=CustomException.class)
    public void updateCustomFieldThrowsException() throws CustomException {
    	//exception.expect(Exception.class);
        CustomFieldRequest request = getRequest();

        when(customService.updateCustomeField(request)).thenThrow(CustomException.class);
        //customController.updateCustomField(request.getId(), request);
    }

I see the test failing with java.lang.AssertionError. I tried the @Rule annotation(shown commented above).

You need a default constructor for CustomException or create the exeception in your test like this: new CustomException("")