There is a missing case here so this doesn't compile

[rogernordquist-tc]

https://github.com/scala/docs.scala-lang/blob/1ae6d880f8a2298ab5150e88740ce5672b16a89a/_overviews/core/futures.md?plain=1#L1184 It should be like:

        completion match {
          case Failure(exception) if exception.getCause != null =>
            println(s"  caused by ${exception.getCause}")
          case _ => ()
        }