Index: modules/field_ui/field_ui.js
===================================================================
RCS file: /cvs/drupal/drupal/modules/field_ui/field_ui.js,v
retrieving revision 1.6
diff -u -r1.6 field_ui.js
--- modules/field_ui/field_ui.js	6 Oct 2010 13:09:11 -0000	1.6
+++ modules/field_ui/field_ui.js	6 Nov 2010 13:49:46 -0000
@@ -118,8 +118,10 @@
       data.tableDrag = tableDrag;
 
       // Create the row handler, make it accessible from the DOM row element.
-      var rowHandler = eval('new rowHandlers.' + data.rowHandler + '(row, data);');
-      $(row).data('fieldUIRowHandler', rowHandler);
+      if (typeof(eval('rowHandlers.' + data.rowHandler)) == 'function') {
+        var rowHandler = eval('new rowHandlers.' + data.rowHandler + '(row, data);');
+        $(row).data('fieldUIRowHandler', rowHandler);
+      }
     });
   },