如何使用Reads解析带有整数列表的JSON

我如何在游戏中构建阅读！2.1.1哪个读取此JSON？下面的示例和代码引发异常。我真的可以在剧中表演！控制台，但如果启动服务器并使用curl，则会出现错误

{
  "title": "title", 
  "description": "description", 
  "categories": [1,3], 
  "sections": [2]
}

遵循游戏指南！网站让我创建了这个“解析器”，但它抛出了一个异常

  implicit val guideReads: Reads[GuideInstance.Update] = (
    (__ \ "title").readNullable[String] ~
    (__ \ "description").readNullable[String] ~
    (__ \ "categories").readNullable(
      Reads.list[Int]
    ) ~
    (__ \ "sections").readNullable(
      Reads.list[Int]
    )
  )(GuideInstance.Update)

例外情况

java.lang.NullPointerException: null
    at play.api.libs.json.Json$.fromJson(Json.scala:90) ~[play_2.10.jar:2.1.1]
    at play.api.libs.json.DefaultReads$$anon$2$$anonfun$10.apply(Reads.scala:453) ~[play_2.10.jar:2.1.1]
.......
    at play.api.libs.json.JsValue$class.validate(JsValue.scala:73) ~[play_2.10.jar:2.1.1]
    at play.api.libs.json.JsObject.validate(JsValue.scala:159) ~[play_2.10.jar:2.1.1]
    at controllers.mtadmin.GuidesController$$anonfun$update$1.apply(GuidesController.scala:114) ~[na:na]
    at controllers.mtadmin.GuidesController$$anonfun$update$1.apply(GuidesController.scala:114) ~[na:na]

---

使用

readNullable[List[Int]]

implicit val guideReads: Reads[GuideInstance.Update] = (
  (__ \ "title").readNullable[String] ~
  (__ \ "description").readNullable[String] ~
  (__ \ "categories").readNullable[List[Int]] ~
  (__ \ "sections").readNullable[List[Int]]
)(GuideInstance.Update)

如果没有，请提供一个更完整的例子，我会帮助你