如何使用读取来解析带有整数列表的JSON

Question

How do I construct a Reads in Play! 2.1.1 which reads this JSON? The example and code below throws an exception. I can actually run it in the Play! console, but if I start the server and use curl I get an error.

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

Following the guide on Play! website made me create this "parser", but it throws an exception.

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

Exception

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]

Answer 1

It should suffice to use 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)

If it doesn't please provide a more complete example and I will help you out!