java - 带有空字段的 Spring MVC JSON 序列化

Question

我试图在 Spring MVC 中将一些对象序列化为 JSON。我使用这种方法：

@Controller
@RequestMapping(produces = "application/json")
public class SurveyAPIController {

    SurveyService surveyService;

    @Autowired
    public SurveyAPIController(SurveyService surveyService) {
        this.surveyService = surveyService;
    }

    //*****************************
    // GET
    //*****************************

    @RequestMapping(value = "/survey/{id}",produces = "application/json;charset=UTF-8")
    @ResponseBody
    public Survey getSurvey(@PathVariable("id") int id) {
        return surveyService.getSurvey(id);
    }
}

Survey 对象中有 Set 字段。如果该 Set 为空，则无法创建 JSON，并且出现此错误：

HTTP 500 - The server encountered an internal error that prevented it from fulfilling this request.

我该如何解决这个问题，？