Jackson's Access.WRITE_ONLY during test null

I'm currently playing around with Jackson's de/serialization features and I encountered a problem, I don't know how to solve.

During my test the @JsonProperty(access = JsonProperty.Access.WRITE_ONLY) annotation is ignored and it only shows null. However with e.g. Postman everything works as expected.

I using just a Spring Boot Starter with Web Starter and Test Starter dependency.

Example Code:

@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

@RestController
class JacksonExampleRestController {

    @PostMapping("/api")
    public void getResti(@RequestBody JacksonModel jacksonModel) {
        System.out.println(jacksonModel.getId());
        System.out.println(jacksonModel.getPassword());
    }
}

class JacksonModel {

    private String id;

    @JsonProperty(access = JsonProperty.Access.WRITE_ONLY)
    private String password;

    public String getId() {
        return id;
    }

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

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

Test:

@RunWith(SpringRunner.class)
@SpringBootTest(classes = DemoApplication.class)
public class DemoApplicationTests {

    private MockMvc mockMvc;

    @Before
    public void setUp() {

        JacksonExampleRestController jacksonExampleRestController = new JacksonExampleRestController();

        mockMvc = MockMvcBuilders.standaloneSetup(jacksonExampleRestController)
                .build();
    }

    @Test
    public void testJackson() throws Exception {
        JacksonModel jacksonModel = new JacksonModel();
        jacksonModel.setId("id");
        jacksonModel.setPassword("password");

        mockMvc.perform(post("/api").
                contentType(APPLICATION_JSON_UTF8)
                .content(convertObjectToJsonBytes(jacksonModel)));
    }

    public static byte[] convertObjectToJsonBytes(Object object)
            throws IOException {
        ObjectMapper mapper = new ObjectMapper();
        mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
        return mapper.writeValueAsBytes(object);
    }
}

Is this the default behaviour and do I have to configure something in my test or is it something else I don't see right now?