Parameters.scala

case class Parameters(userId: UserId,
                      device: Option[Device] = None,
                      additionalParameters: Map[String, Iterable[String]] = Map.empty) {
  def getParameter[T](name: String, default: T)(implicit converter: (Iterable[String]) => Option[T]): T = {
    additionalParameters.get(name).flatMap(converter).getOrElse(default)
  }
}

object Parameters {
  implicit val strings2Int = (values: Iterable[String]) => {
    import scala.util.control.Exception.catching
    catching(classOf[NumberFormatException]) opt values.head.trim.toInt
  }
}

Parameters2.scala

case class Parameters(userId: UserId,
                      device: Option[Device] = None,
                      additionalParameters: Map[String, Iterable[String]] = Map.empty) {
  def getParameter[T](name: String, default: T)(implicit converter: SafeConverter[Iterable[String], T]): T = {
    additionalParameters.get(name).flatMap(converter.convert).getOrElse(default)
  }
}

case class SafeConverter[A, B](val convert: A => Option[B]) extends AnyVal

object SafeConverter {
  implicit val strings2Int = SafeConverter((values: Iterable[String]) => {
    import scala.util.control.Exception.catching
    catching(classOf[NumberFormatException]) opt values.head.trim.toInt
  })
}