play List JSON serialization

gistfile1.txt

No Json deserializer found for type List[models.Subscription]. Try to implement an implicit Writes or Format for this type.
In /Volumes/HD/Users/nicolas/Boulot/cloudbees/je-sp/app/controllers/API.scala at line 25.

val subscriptions: List[Subscription] =  ???

22          Ok(
23            Json.obj("account" -> account.getName,
24                     "salesforce_id" -> account.getId,
25                     "subscriptions" -> subscriptions, 
26                     "licenses" -> "TODO",
27                     "credits" -> "TODO")

class Subscription(...) extends Writes[Subscription]{
  def writes(o: Subscription): JsValue = {
    Json.obj(
      "product" -> product,
      "expiration" -> FastDateFormat.getInstance("dd-MM-yyyy").format(expiration))
  }
}

You can also try if you don't want to implement your own Writer

implicit val subscriptionFormat = Json.format[Subscription]