Index: misc/tableheader.js
===================================================================
RCS file: /cvs/drupal/drupal/misc/tableheader.js,v
retrieving revision 1.11
diff -u -p -r1.11 tableheader.js
--- misc/tableheader.js	10 Jan 2008 17:59:38 -0000	1.11
+++ misc/tableheader.js	11 Jan 2008 21:05:06 -0000
@@ -19,7 +19,7 @@ Drupal.behaviors.tableHeader = function 
 
     // Sets an id for cloned table header.
     var headerID = headerClone.attr('id');
-    if (headerID != '') {
+    if (typeof(headerID) != 'undefined') {
       headerClone.attr('id', headerID + '-header');
     }