Showing that you need to remember to add the None case to your extractor

ExtractorOptionNeedsNoneCase.scala

  object ExtTest {
    def unapply(arg: Int): Option[Int] = arg match {
      case a if a < 5 => Some(a)
    }
  }

  val x = 3
  x match {
    case ExtTest(a) => println(a)
  }

  val y = 10
  y match {
    case ExtTest(a) => println(a)
      // This will result in a MatchError
  }

At least, you need to appropriately generate None, whether or not it is through a case clause.