Filtering out null JSON fields

example.scala

import play.api.libs.json._

object Example extends App {

  case class EmailPerformanceInfo(campaignCount: Int, name: Option[String])

  implicit val emailPerformanceInfoWrites = new Writes[EmailPerformanceInfo] {
    def writes(info: EmailPerformanceInfo): JsValue = {
      import info._
      Json.obj(
        "campaignCount" -> campaignCount,
        "fancyName"     -> name // NB: this may turn into null in the JSON
        )
    }
  }

  // Remove null values from JSON (could pimp onto JsValue if you wanted)
  def withoutNull(json: JsValue): JsValue = json match {
    case JsObject(fields) =>
      JsObject(fields.flatMap {
        case (_, JsNull)          => None // could match on specific field name here
        case other @ (name,value) => Some(other) // consider recursing on the value for nested objects
      })
    case other => other
  }

  val withName = EmailPerformanceInfo(1,   Some("Bob"))
  val noName =   EmailPerformanceInfo(100, None       )

  println(withoutNull(Json.toJson(withName)))
  // -> {"campaignCount":1,"fancyName":"Bob"}

  println(withoutNull(Json.toJson(noName)))
  // -> {"campaignCount":100}

  // What we really want is nullable handling in Json.obj:
  // https://groups.google.com/forum/#!topic/play-framework-dev/o3ElehlHafM
  // https://groups.google.com/d/msg/play-framework/J6nAAVJKXIE/r4XXNtty2McJ

}

Similar solutions at http://stackoverflow.com/questions/24512942/play-how-to-remove-the-fields-without-value-from-json-and-create-a-new-json-wit. For just JsObject, filter is slightly simpler.