Type safe "optional" field

TypesafeField.scala

sealed trait FT {
  type VT
}
object FT {
  sealed trait Concrete extends FT {
    override type VT = Nothing
  }

  case object Concrete extends Concrete
  sealed trait Derived extends FT {
    override type VT = Int
  }

  case object Derived extends Derived
}

trait Field[T <: FT] {
  def name: String
  def version: T#VT
}

object Field {
  def derived(
    fieldName:    String,
    fieldVersion: Int
  ): Field[FT.Derived] = new Field[FT.Derived] {
    override val name:    String = fieldName
    override val version: Int    = fieldVersion
  }

  def concrete(fieldName: String): Field[FT.Concrete] = new Field[FT.Concrete] {
    override val name:    String  = fieldName
    override def version: Nothing = ???
  }
}