Play 2.3 implicit json conversion causes null pointer exception

Question

I\'m trying to parse json into my case class DealFormMap

case class DealFormMap(limit: Option[Int], filter: Option[DealFormFilterMap])
case clas         


        

Answer 1

The problem is the initialization order. dealFormMapReads depends on the implicit dealFormFilterMapReads, which isn't defined until after. It will compile because the implicit is found, even though it hasn't been initialized, so dealFormMapReads is read as null, which eventually causes the NPE.

Lazily loading will fix it:

implicit val dealFormMapReads: Reads[DealFormMap] = (
     (JsPath \ "limit").readNullable[Int] and
     (JsPath \ "filter").lazyReadNullable[DealFormFilterMap](dealFormFilterMapReads)
)(DealFormMap)

Or you could just swap the order in which the Reads are defined.

---

The NPE thrown here is similar to this example:

case class A(i: Int)

object Test {
     val test = a.toString
     val a = A(1)
}

// Compiles up to here

Test.test // throws NPE, because `a` was not initialized before `test`