How Test PUT RestController in Spring Boot - testing

Question

How can I test one PUT request with Spring Boot??
I have this method:
#RequestMapping(method = RequestMethod.PUT, value = "/")
public NaturezaTitulo save(#RequestBody NaturezaTitulo naturezaTitulo){
return naturezaTituloService.save(naturezaTitulo);
}
and this test class:
#RunWith(SpringJUnit4ClassRunner.class)
#SpringApplicationConfiguration(classes = Application.class)
#WebAppConfiguration
public class NaturezaTituloControllerTest {
private MediaType contentType = new MediaType(MediaType.APPLICATION_JSON.getType(),
MediaType.APPLICATION_JSON.getSubtype(),
Charset.forName("utf8"));
private MockMvc mockMvc;
private HttpMessageConverter mappingJackson2HttpMessageConverter;
private List<NaturezaTitulo> naturezaTituloList = new ArrayList<>();
#Autowired
private WebApplicationContext webApplicationContext;
#Autowired
void setConverters(HttpMessageConverter<?>[] converters) {
this.mappingJackson2HttpMessageConverter = Arrays.asList(converters).stream().filter(
hmc -> hmc instanceof MappingJackson2HttpMessageConverter).findAny().get();
Assert.assertNotNull("the JSON message converter must not be null",
this.mappingJackson2HttpMessageConverter);
}
#Before
public void setup() throws Exception {
this.mockMvc = webAppContextSetup(webApplicationContext).build();
}
#Test
public void naturezaTituloNotFound() throws Exception {
mockMvc.perform(get("/naturezatitulo/55ce2dd6222e629f4b8d6fe0"))
.andExpect(status().is4xxClientError());
}
#Test
public void naturezaTituloSave() throws Exception {
NaturezaTitulo naturezaTitulo = new NaturezaTitulo();
naturezaTitulo.setNatureza("Testando");
mockMvc.perform(put("/naturezatitulo/").content(this.json(naturezaTitulo))
.contentType(contentType))
.andExpect(jsonPath("$.id", notNullValue()));
}
protected String json(Object o) throws IOException {
MockHttpOutputMessage mockHttpOutputMessage = new MockHttpOutputMessage();
this.mappingJackson2HttpMessageConverter.write(
o, MediaType.APPLICATION_JSON, mockHttpOutputMessage);
return mockHttpOutputMessage.getBodyAsString();
}
}
but I got this error:
java.lang.IllegalArgumentException: json can not be null or empty at
com.jayway.jsonpath.internal.Utils.notEmpty(Utils.java:259)
how can I pass one object from body in Put test?
tks