play-json_nullFields

import play.api.libs.json._
import play.api.libs.functional.syntax._

case class User(id: Int, name: String, partner: Option[String])

// Json format without null
val userReads: Reads[User] = (
  (JsPath \ "id").read[Int] and
  (JsPath \ "name").read[String] and
  (JsPath \ "partner").readNullable[String]
)(User.apply _)

val userWrites: Writes[User] = (
  (JsPath \ "id").write[Int] and
  (JsPath \ "name").write[String] and
  (JsPath \ "partner").writeNullable[String]
)(unlift(User.unapply))

val userFormat: Format[User] = Format(userReads, userWrites)

// Json format with null
val userReadsNull: Reads[User] = (
  (JsPath \ "id").read[Int] and
  (JsPath \ "name").read[String] and
  (JsPath \ "partner").read[Option[String]]
)(User.apply _)

val userWritesNull: Writes[User] = (
  (JsPath \ "id").write[Int] and
  (JsPath \ "name").write[String] and
  (JsPath \ "partner").write[Option[String]]
)(unlift(User.unapply))

val userFormatNull: Format[User] = Format(userReadsNull, userWritesNull)


// demo time
val user1 = User(123, "John", Some("Mary"))
val user2 = User(123, "Peter", None)

Json.toJson(user1)(userFormat)
Json.toJson(user2)(userFormat)

Json.toJson(user1)(userFormatNull)
Json.toJson(user2)(userFormatNull)