playframework 2.0 - slick2 + play2 returns a collection of objects json format error -

slick code:

case class user(id: option[int], name: option[string])  class usertable(tag: tag) extends table[user](tag, "app_user") {     def id = column[int]("id", o.primarykey, o.autoinc)     def name = column[string]("name", o.nullable, o.dbtype("varchar(8)"))     override def * = (id.?, name.?) <> (user.tupled, user.unapply _) }  object userhelper {     val quser = tablequery[usertable]     def all: list[user] = db withsession { implicit session =>         quser.list.map(u => user.tupled(u.id, u.name))     } } 

play code:

object usercontroller extends controller {     def index = action {         ok(json.tojson(userhelper.all))     } } 

compilation error:

no json deserializer found type list[user]. try implement implicit writes or format type.