An example of an abstract class definition breaking compilation of spray-shapeless dependent code

abstractClassTest.scala

import fommil.sjs.FamilyFormats
import shapeless.cachedImplicit
import spray.json.{DefaultJsonProtocol, RootJsonFormat}

sealed trait SomeTrait {
  def key: String
  def value: String
}

// compiles
class SomeClass(override val key: String, override val value: String) extends SomeTrait

case class SomeCaseClass(override val key: String, override val value: String) extends SomeTrait

case object SomeSingleton extends SomeClass("b", "c")

object TestValue {
  val a = new SomeClass("a", "b")
  val b = SomeCaseClass("a", "b")
  val d = SomeSingleton
}

/*
abstract class SomeAbstractClass(override val key: String, override val value: String) extends SomeTrait // does not compile
case object SomeAbstractSingleton extends SomeAbstractClass("b", "c")
*/

object TestFormats extends DefaultJsonProtocol with FamilyFormats {
  implicit val crmReasonFormats: RootJsonFormat[SomeTrait] = cachedImplicit
}