How to suppress "match is not exhaustive!" warning in Scala

How can I suppress the "match is not exhaustive!" warning in the following Scala code?

val l = "1" :: "2" :: Nil
l.sliding(2).foreach{case List(a,b) => }

The only solution that I found so far is to surround the pattern matching with an additional match statement:

l.sliding(2).foreach{x => (x: @unchecked) match {case List(a,b) => }}

However this makes the code unnecessarily complex and pretty unreadable. So there must be a shorter and more readable alternative. Does someone know one?

Edit

I forgot to mention that my list l has at least 2 elements in my program. That's why I can safely suppress the warning.