src/Pure/Admin/build_fonts.scala

     sources: List[Family] = default_sources,
     source_dirs: List[Path] = Nil,
     target_prefix: String = "Isabelle",
     target_version: String = "",
     target_dir: Path = default_target_dir,
-    progress: Progress = No_Progress)
+    progress: Progress = new Progress)
   {
     progress.echo("Directory " + target_dir)
     hinting.foreach(hinted => Isabelle_System.mkdirs(target_dir + hinted_path(hinted)))
 
     val font_dirs = source_dirs ::: List(Path.explode("~~/Admin/isabelle_fonts"))