Test showing classes with an option[JsonNode] stopped serializing

JsonNodeOptionDeserializerTest.scala

import com.fasterxml.jackson.databind.{ObjectMapper, JsonNode}
import scala.Some
import org.specs2.mutable.SpecificationWithJUnit
import com.fasterxml.jackson.module.scala.DefaultScalaModule

class JsonNodeOptionDeserializerTest extends SpecificationWithJUnit {
  "Option[JsonNode] " should {
    "serialize its content when contained in an object" in {
      val mapper = new ObjectMapper().registerModule(DefaultScalaModule)
      val json: String = """{"prop":"value"}"""
      val tree: JsonNode = mapper.readTree( json)
      val wrapperOfOptionOfJsonNode = WrapperOfOptionOfJsonNode(Some(tree))

      val actualJson: String = mapper.writeValueAsString(wrapperOfOptionOfJsonNode)

      actualJson mustEqual """{"jsonNode":{"prop":"value"}}"""
    }
  }
}
case class WrapperOfOptionOfJsonNode(jsonNode: Option[JsonNode])