Index: drupal-6.x-dev/includes/common.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/common.inc,v
retrieving revision 1.702
diff -u -p -r1.702 common.inc
--- drupal-6.x-dev/includes/common.inc	17 Oct 2007 21:59:31 -0000	1.702
+++ drupal-6.x-dev/includes/common.inc	19 Oct 2007 07:14:13 -0000
@@ -3140,7 +3140,7 @@ function drupal_write_record($table, &$o
     if ($info['type'] == 'serial') {
       $serials[] = $field;
       // Ignore values for serials when inserting data. Unsupported.
-      $object->$field = 'NULL';
+      unset($object->$field);
     }
 
     // Build arrays for the fields, placeholders, and values in our query.