MethodArgumentTypeMismatchException при работе с OffsetDateTime

Тестирую такой контроллер

    @Override
    @PostMapping(value = "/postTest")
    public Long postTest(
            @RequestBody @Valid SomeObject so,
            @RequestParam(value = "period", required = true) @NotNull OffsetDateTime period)
            throws ApiFault {
        return service.post(so, convertToDate(period));
    }

тест

    @Test
    public void createRegistryHeader() throws Exception {

        ZoneId cet = ZoneId.of("CET");
        OffsetDateTime now = OffsetDateTime.now(cet).truncatedTo(ChronoUnit.MILLIS);
        String s = DateTimeFormatter.ISO_LOCAL_DATE_TIME.format(period);
        SomeObject so = // создание и наполнение объекта
        MvcResult result = this.mockMvc.perform(post("/rs/postTest")
                .accept(MediaType.APPLICATION_JSON)
                .contentType(MediaType.APPLICATION_JSON_VALUE)
                .content(asJsonString(so))
                .param("period", s)).andDo(print())
                .andExpect(status().isOk())
                .andReturn();

        // прочая логика
    }

падает с

Async:
    Async started = false
     Async result = null

Resolved Exception:
             Type = org.springframework.web.method.annotation.MethodArgumentTypeMismatchException

ModelAndView:
        View name = null
             View = null
            Model = null

FlashMap:
       Attributes = null

MockHttpServletResponse:
           Status = 400
    Error message = null
          Headers = {}
     Content type = null
             Body = 
    Forwarded URL = null
   Redirected URL = null
          Cookies = []

Status expected:<200> but was:<400>
Expected :200
Actual   :400