Customize upickle to support both null and empty bracket [] as None

[kaitks]

Convert [] as None is the default behavior of upickle, and per document I managed to convert null to None by using an customized upickle

object OptionPickler extends upickle.AttributeTagged {
  override implicit def OptionWriter[T: Writer]: Writer[Option[T]] =
    implicitly[Writer[T]].comap[Option[T]] {
      case None => null.asInstanceOf[T]
      case Some(x) => x
    }

  override implicit def OptionReader[T: Reader]: Reader[Option[T]] = {
    new Reader.Delegate[Any, Option[T]](implicitly[Reader[T]].map(Some(_))){
      override def visitNull(index: Int) = None
    }
  }
}

How to make a custom upickle that can convert both null and [] to None?