Simple enums are (de)serialized as JSON strings.
By "simple" we mean an enum that only has "singleton cases" as defined in the docs.
That is, enum who's cases don't have a parameter clause.

      enum Semaphore derives JsonRW:
        case Red, Yellow, Green

      val semaphore = Semaphore.Red
      println(semaphore.toJson)
      // "Red"