Index: openacs-4/packages/xowiki/tcl/xowiki-www-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/xowiki/tcl/xowiki-www-procs.tcl,v
diff -u -r1.368.2.52 -r1.368.2.53
--- openacs-4/packages/xowiki/tcl/xowiki-www-procs.tcl	26 Nov 2019 12:54:00 -0000	1.368.2.52
+++ openacs-4/packages/xowiki/tcl/xowiki-www-procs.tcl	26 Jan 2020 16:48:40 -0000	1.368.2.53
@@ -2891,10 +2891,12 @@
     set f [::xowiki::formfield::submit_button new -destroy_on_cleanup \
                -name __form_button_ok \
                -CSSclass $CSSclass]
-
-    ::html::div -class [$f form_button_wrapper_CSSclass] {
-      $f render_input
-    }
+    
+    ::html::div [expr {[$f exists form_button_wrapper_CSSclass]
+                       ? [list class [$f form_button_wrapper_CSSclass]]
+                       : {} }] {
+                         $f render_input
+                       }
   }
 
   FormPage instproc form_fields_sanity_check {form_fields} {