Cannot convert nested Maps into json

[velvia]

Hi, I'm using spray-json 1.2.2 and get this error:

scala> Map("a" -> Map("b" -> 2), "b" -> Map()).toJson
:14: error: Cannot find JsonWriter or JsonFormat type class for scala.collection.immutable.Map[String,scala.collection.immutable.Map[_ <: String, Int]]
Map("a" -> Map("b" -> 2), "b" -> Map()).toJson
^
Doesn't seem like it should be that hard to fix.

[jrudolph]

Right, mapFormat seems a bit broken requiring a JsonFormat[K] for the key. We cannot fix this right now as it would break binary compatibility.

[ancane]

Looks like heterogeneous map involved in this example. I guess, spray-json-shapeless could handle that.

Regular nested maps work fine though:

scala> Map("a" -> Map("b" -> 2), "b" -> Map("c" -> 3)).toJson
res0: spray.json.JsValue = {"a":{"b":2},"b":{"c":3}}

Seems like it's not a bug. Thanks.