我在下面的行中得到NullPointerException。我已经分别打印了requestJson，并且产生了结果。

this.mockMvc.perform(post("http://localhost:9004/api/msg/inf").content(requestJson).contentType(MediaType.APPLICATION_JSON)).andExpect(status().isOk()); 

requestJson的生成方式如下：

ObjectMapper mapper = new ObjectMapper().registerModule(new ParameterNamesModule())
.registerModule(new Jdk8Module())
.registerModule(new JavaTimeModule());

mapper.findAndRegisterModules();

mapper.registerModule(new JavaTimeModule());
mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS,false);

 mapper.configure(SerializationFeature.WRAP_ROOT_VALUE,false);
    ObjectWriter ow = mapper.writer().withDefaultPrettyPrinter();
    String requestJson=ow.writeValueAsString(inflow);

当我打印requestJson时，它显示以下内容：

{"type":"inflow","order":"OE12345","amount":10002,"deliveryDate":"2019-11-15T12:11:45.534"}