NPE when Json.toJson

[He-Pin]

Caused by: java.lang.NullPointerException
    at play.api.libs.json.LowPriorityWrites.$anonfun$traversableWrites$2(Writes.scala:307)
    at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:234)
    at scala.collection.mutable.ResizableArray.foreach(ResizableArray.scala:59)
    at scala.collection.mutable.ResizableArray.foreach$(ResizableArray.scala:52)
    at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
    at scala.collection.TraversableLike.map(TraversableLike.scala:234)
    at scala.collection.TraversableLike.map$(TraversableLike.scala:227)
    at scala.collection.AbstractTraversable.map(Traversable.scala:104)
    at play.api.libs.json.LowPriorityWrites.$anonfun$traversableWrites$1(Writes.scala:307)
    at play.api.libs.json.Writes$$anon$6.writes(Writes.scala:142)
    at play.api.libs.json.PathWrites.$anonfun$nullable$2(JsConstraints.scala:184)
    at play.api.libs.json.OWrites$$anon$3.writes(Writes.scala:111)
    at play.api.libs.json.OWrites$MergedOWrites$.mergeIn(Writes.scala:75)
    at play.api.libs.json.OWrites$MergedOWrites$$anon$1.writeFields(Writes.scala:67)
    at play.api.libs.json.OWrites$MergedOWrites$$anon$1.writeFields(Writes.scala:63)
    at play.api.libs.json.OWrites$MergedOWrites$.mergeIn(Writes.scala:73)
    at play.api.libs.json.OWrites$MergedOWrites$$anon$1.writeFields(Writes.scala:66)
    at play.api.libs.json.OWrites$MergedOWrites$$anon$1.writeFields(Writes.scala:63)
    at play.api.libs.json.OWrites$OWritesFromFields.writes(Writes.scala:95)
    at play.api.libs.json.OWrites$OWritesFromFields.writes$(Writes.scala:93)
    at play.api.libs.json.OWrites$MergedOWrites$$anon$1.writes(Writes.scala:63)
    at play.api.libs.json.OWrites$$anon$2.$anonfun$contramap$1(Writes.scala:106)
    at play.api.libs.json.OWrites$$anon$3.writes(Writes.scala:111)
    at play.api.libs.json.OWrites$$anon$3.writes(Writes.scala:110)
    at play.api.libs.json.LowPriorityWrites.$anonfun$traversableWrites$2(Writes.scala:307)
    at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:234)
    at scala.collection.mutable.ResizableArray.foreach(ResizableArray.scala:59)
    at scala.collection.mutable.ResizableArray.foreach$(ResizableArray.scala:52)
    at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
    at scala.collection.TraversableLike.map(TraversableLike.scala:234)
    at scala.collection.TraversableLike.map$(TraversableLike.scala:227)
    at scala.collection.AbstractTraversable.map(Traversable.scala:104)
    at play.api.libs.json.LowPriorityWrites.$anonfun$traversableWrites$1(Writes.scala:307)
    at play.api.libs.json.Writes$$anon$6.writes(Writes.scala:142)
    at play.api.libs.json.Json$.toJson(Json.scala:186)
    at controllers.FacadesController.$anonfun$queryTypes$2(FacadesController.scala:28)

[He-Pin]

[He-Pin]

The root cause is I am using a Recursive Types and auto mapping, so boom! The automapping gave me a Writes, but with the recursived one as null.

[He-Pin]

easy fixed with a lazy.

1. The macro should throw exception when auto mapping the recursive type.
2. When the Writes is null,throw an exception.
3. Yes,two lazy vals will give a SOF, eg:

   java.lang.StackOverflowError
   at scala.collection.SeqLike.$colon$plus$(SeqLike.scala:559)
   at scala.collection.AbstractSeq.$colon$plus(Seq.scala:41)
   at play.api.libs.json.JsPath.$bslash(JsPath.scala:186)
   at services.schema.FieldDescription$.writes$lzycompute(SchemaManager.scala:234)
   at services.schema.FieldDescription$.writes(SchemaManager.scala:234)
   at services.schema.TypeDescription$.writes$lzycompute(SchemaManager.scala:198)
   at services.schema.TypeDescription$.writes(SchemaManager.scala:198)

[cchantep]

Hi @hepin1989, the macro could check for direct reference to the same type (which anyway lead to issue in Scala), on the other side indirect reference using Option or Traversable could be supported.