src/Pure/System/isabelle_system.scala

--- a/src/Pure/System/isabelle_system.scala	Sat Apr 09 15:35:27 2022 +0200
+++ b/src/Pure/System/isabelle_system.scala	Sat Apr 09 15:40:29 2022 +0200
@@ -484,7 +484,7 @@
   object Download extends Scala.Fun("download", thread = true) {
     val here = Scala_Project.here
     override def invoke(args: List[Bytes]): List[Bytes] =
-      args match { case List(url) => List(download(url.text).bytes) case _ => ??? }
+      args.map(url => download(url.text).bytes)
   }