src/HOL/Tools/Mirabelle/mirabelle.scala

--- a/src/HOL/Tools/Mirabelle/mirabelle.scala	Sat May 15 13:25:52 2021 +0200
+++ b/src/HOL/Tools/Mirabelle/mirabelle.scala	Sat May 15 17:38:49 2021 +0200
@@ -213,8 +213,7 @@
       "x:" -> (arg => exclude_sessions = exclude_sessions ::: List(arg)))
 
     val sessions = getopts(args)
-
-    if (actions.isEmpty) error("Missing actions (option -A)")
+    if (actions.isEmpty) getopts.usage()
 
     val progress = new Console_Progress(verbose = verbose)