org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON

记一次踩坑经历：
Resolved [org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: (was java.lang.NullPointerException); nested exception is com.fasterxml.jackson.databind.JsonMappingException: (was java.lang.NullPointerException) (through reference chain: com.renqijie.pojo.vo.IndexBean["images"]->java.util.ArrayList[0]->com.renqijie.pojo.Image["id"])]

原因：
JavaBean类Image中有一个属性类型刚开始设置成int类型，生成getter/setter方法后，又将其改成了Integer类型，结果就出现了上述情况