Index: includes/common.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/common.inc,v
retrieving revision 1.1164
diff -u -p -r1.1164 common.inc
--- includes/common.inc	16 May 2010 19:21:45 -0000	1.1164
+++ includes/common.inc	17 May 2010 00:41:56 -0000
@@ -5426,7 +5426,7 @@ function element_children(&$elements, $s
   $children = array();
   $sortable = FALSE;
   foreach ($elements as $key => $value) {
-    if ($key[0] !== '#') {
+    if ($key === '' || $key[0] !== '#') {
       $children[$key] = $value;
       if (is_array($value) && isset($value['#weight'])) {
         $sortable = TRUE;