Cannot serialize Option[Foo] if Foo is a trait

[miracle2121]

I've encountered an issue where I cannot serialize an Option wrapping a trait. I'm using version 2.2.2. Is this behavior expected?

import com.fasterxml.jackson.module.scala.DefaultScalaModule
import com.fasterxml.jackson.databind.ObjectMapper

trait MyTrait {
  def myval: String
}

case class MyImpl(myval: String) extends MyTrait

case class Wrapper1(
  mytrait: Option[MyTrait]
)

case class Wrapper2(
  myimpl: Option[MyImpl]
)

case class Wrapper3(
  mytraits: Option[List[MyTrait]]
)

val obj1 = Wrapper1(
  mytrait = Some(
    MyImpl(
      myval = "MyVal1"
    )
  )
)

val obj2 = Wrapper2(
  myimpl = Some(
    MyImpl(
      myval = "MyVal2"
    )
  )
)

val obj3 = Wrapper3(
  mytraits = Some(
    List(
      MyImpl(
        myval = "MyVal3"
      )
    )
  )
)

val mapper = new ObjectMapper()
mapper.registerModule(DefaultScalaModule)

mapper.writeValueAsString(obj1) // throws exception below
mapper.writeValueAsString(obj2) // works as expected
mapper.writeValueAsString(obj3) // works as expected

This is the stack trace:

java.lang.InternalError: Malformed class name
    at java.lang.Class.getSimpleName(Class.java:1133)
    at com.fasterxml.jackson.databind.JsonMappingException$Reference.toString(JsonMappingException.java:108)
    at com.fasterxml.jackson.databind.JsonMappingException._appendPathDesc(JsonMappingException.java:364)
    at com.fasterxml.jackson.databind.JsonMappingException.getPathReference(JsonMappingException.java:267)
    at com.fasterxml.jackson.databind.JsonMappingException._buildMessage(JsonMappingException.java:340)
    at com.fasterxml.jackson.databind.JsonMappingException.getMessage(JsonMappingException.java:321)
    at com.fasterxml.jackson.databind.JsonMappingException.toString(JsonMappingException.java:348)
    at java.lang.String.valueOf(String.java:2826)
    at java.io.PrintWriter.println(PrintWriter.java:710)
    at java.lang.Throwable.printStackTrace(Throwable.java:509)
    at scala.tools.nsc.util.package$$anonfun$stackTraceString$1.apply(package.scala:84)
    at scala.tools.nsc.util.package$$anonfun$stackTraceString$1.apply(package.scala:84)
    at scala.tools.nsc.util.package$.stringFromWriter(package.scala:73)
    at scala.tools.nsc.util.package$.stackTraceString(package.scala:84)
    at scala.tools.nsc.interpreter.IMain$ReadEvalPrint$$anonfun$bindError$2.apply(IMain.scala:714)
    at scala.tools.nsc.interpreter.IMain$ReadEvalPrint$$anonfun$bindError$2.apply(IMain.scala:714)
    at scala.tools.nsc.interpreter.ReplConfig$$anonfun$logAndDiscard$1.applyOrElse(ReplConfig.scala:46)
    at scala.tools.nsc.interpreter.ReplConfig$$anonfun$logAndDiscard$1.applyOrElse(ReplConfig.scala:41)
    at scala.runtime.AbstractPartialFunction.apply(AbstractPartialFunction.scala:33)
    at scala.tools.nsc.interpreter.IMain.scala$tools$nsc$interpreter$IMain$$withLastExceptionLock(IMain.scala:250)
    at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.bindError(IMain.scala:711)
    at scala.tools.nsc.interpreter.IMain$Request.loadAndRun(IMain.scala:984)
    at scala.tools.nsc.interpreter.IMain.loadAndRunReq$1(IMain.scala:573)
    at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:604)
    at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:568)
    at scala.tools.nsc.interpreter.ILoop.reallyInterpret$1(ILoop.scala:756)
    at scala.tools.nsc.interpreter.ILoop.interpretStartingWith(ILoop.scala:801)
    at scala.tools.nsc.interpreter.ILoop.command(ILoop.scala:713)
    at scala.tools.nsc.interpreter.ILoop.processLine$1(ILoop.scala:577)
    at scala.tools.nsc.interpreter.ILoop.innerLoop$1(ILoop.scala:584)
    at scala.tools.nsc.interpreter.ILoop.loop(ILoop.scala:587)
    at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply$mcZ$sp(ILoop.scala:878)
    at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:833)
    at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:833)
    at scala.tools.nsc.util.ScalaClassLoader$.savingContextLoader(ScalaClassLoader.scala:135)
    at scala.tools.nsc.interpreter.ILoop.process(ILoop.scala:833)
    at scala.tools.nsc.interpreter.ILoop.main(ILoop.scala:900)
    at xsbt.ConsoleInterface.run(ConsoleInterface.scala:69)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at sbt.compiler.AnalyzingCompiler.call(AnalyzingCompiler.scala:102)
    at sbt.compiler.AnalyzingCompiler.console(AnalyzingCompiler.scala:77)
    at sbt.Console.sbt$Console$$console0$1(Console.scala:23)
    at sbt.Console$$anonfun$apply$2$$anonfun$apply$1.apply$mcV$sp(Console.scala:24)
    at sbt.Console$$anonfun$apply$2$$anonfun$apply$1.apply(Console.scala:24)
    at sbt.Console$$anonfun$apply$2$$anonfun$apply$1.apply(Console.scala:24)
    at sbt.Logger$$anon$4.apply(Logger.scala:90)
    at sbt.TrapExit$App.run(TrapExit.scala:244)
    at java.lang.Thread.run(Thread.java:662)

[christophercurrie]

Not expected; I'll try and track down what's causing this for the next release.

[christophercurrie]

I can reproduce this error, but only (a) on 2.2.x, (b) using Scala 2.10, (c) in paste mode on the REPL. Running your example as a unit test on 2.2.2 using Scala 2.10 doesn't trigger the error, nor does using the REPL on 2.3+. Given that 2.3 is at this point over a year old, I'd recommend upgrading, if the REPL is an important part of your workflow.