Index: openacs-4/packages/acs-admin/www/apm/version-callback-add-edit.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-admin/www/apm/version-callback-add-edit.tcl,v
diff -u -N -r1.12 -r1.12.2.1
--- openacs-4/packages/acs-admin/www/apm/version-callback-add-edit.tcl	7 Aug 2017 23:47:45 -0000	1.12
+++ openacs-4/packages/acs-admin/www/apm/version-callback-add-edit.tcl	13 Mar 2019 09:40:42 -0000	1.12.2.1
@@ -74,7 +74,9 @@
     }
     {proc
 	{ [apm_callback_has_valid_args -type $type -proc_name $proc] }
-	{The callback proc $proc must be defined with ad_proc [ad_decode [apm_arg_names_for_callback_type -type $type] "" "and should take no arguments" "and have the following required switches: [apm_arg_names_for_callback_type -type $type]"]}
+	{The callback proc $proc must be defined with ad_proc [expr {[apm_arg_names_for_callback_type -type $type] eq "" ?
+                                                                     "and should take no arguments" :
+                                                                     "and have the following required switches: [apm_arg_names_for_callback_type -type $type]"}]}
     }
 } -on_submit {