play-jsonでnullの含まれるListをパースする ref: http://qiita.com/kakakazuma/items/7cf60811f616d1c40147

error

No Json deserializer found for type Seq[Option[String]]. Try to implement an implicit Reads or Format for this type.
[error]       (JsPath \ "params").read[Seq[Option[String]]] | Reads.pure(Seq.empty[Option[String]])

parseResult

Sample(aaa,18,ListBuffer(Some(test1), None, Some(test2)))

sample.json

{
 "id":"aaa",
 "age":18,
 "params":[
  "test1",
  null,
  "test2"
 ]
}

Sample.scala

case class Sample(id:String, age:Int, params:Seq[Option[String]])

object Sample extends ((String,Int,Seq[Option[String]]) => Sample) {

  implicit val SeqOpStringRead = new Reads[Seq[Option[String]]] {
    override def reads(json: JsValue): JsResult[Seq[Option[String]]] = {
      json match {
        case JsArray(seq) => JsSuccess(seq.map(jsvalue => jsvalue.asOpt[String]))
        case _ => JsError("Invalid array")
      }
    }
  }

  implicit val SampleRead: Reads[Sample] = (
    (JsPath \ "id").read[String] and
      (JsPath \ "age").read[Int] and
      (JsPath \ "params").read[Seq[Option[String]]] | Reads.pure(Seq.empty[Option[String]])
    )(Sample)
}