JsonMappingException try trying to use jacks test methods

[simbo1905]

(My apologies if this is just a simple mistake on my part as I am new to scala)

I checkout and build jacks and added two of my own classes into the file test.scala:

abstract class Message
case class CardDrawn(player: Long, card: Int, mType: String = "CardDrawn") extends Message
case class CardSet(cards: List[CardDrawn], mType: String = "CardSet") extends Message

And then added in a test to check that they roundtrip fine.

test("cardset works"){
    rw(CardSet(List(CardDrawn(1L,2),CardDrawn(3L,4)))) should equal (CardSet(List(CardDrawn(1L,2),CardDrawn(3L,4))))

    val cs = CardSet(List(CardDrawn(1L,2),CardDrawn(3L,4)))
    val json = write(cs)
    val obj = read(json)
    cs should equal (obj)
  }

The firs call to "rw()" works suggesting that all is very well indeed. The following lines where I try to explicitly to the read and write (the same operations as the rw call) gets an exception:

Can not instantiate abstract type [simple type, class scala.runtime.Nothing$] (need to add/enable type information?)
 at [Source: java.io.StringReader@76d26a; line: 1, column: 2]
com.fasterxml.jackson.databind.JsonMappingException: Can not instantiate abstract type [simple type, class scala.runtime.Nothing$] (need to add/enable type information?)
 at [Source: java.io.StringReader@76d26a; line: 1, column: 2]
    at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:164)
    at com.fasterxml.jackson.databind.deser.std.ThrowableDeserializer.deserializeFromObject(ThrowableDeserializer.java:77)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:121)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2888)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2048)
    at com.lambdaworks.jacks.JacksMapper$class.readValue(jacks.scala:20)
    at com.lambdaworks.jacks.JacksMapper$.readValue(jacks.scala:40)
    at com.lambdaworks.jacks.JacksTestSuite$class.read(test.scala:287)
    at com.lambdaworks.jacks.CaseClassSuite.read(test.scala:91)

Whats the correct way to roundtrip such a structured class and is there something wrong with the rw method which is masking an issue?