object Test {
  type Id[X] = X

  def main(args: Array[String]) {
    val a: Id[Option[Int]] = None

    a match {
      case Some(x) => println(x)
      case None => println("Nothing")
    }
  }
}

$ sbt run
[info] Set current project to default-2e4ad8 (in build file:../)
[info] Compiling 1 Scala source to .../target/scala-2.10/classes...
[warn] .../src/main/scala/Test.scala:9: unreachable code
[warn]       case None => println("Nothing")
[warn]                           ^
[warn] one warning found
[info] Running Test 
Nothing

type Id[X] = Option[X]

val a: Id[Int] = None