mysql error when saving node

I get an error when saving nodes. I've changed the weight of the following rows in the system table to 1 from 0:

xmlsitemap |
xmlsitemap_engines
xmlsitemap_node
xmlsitemap_term
xmlsitemap_user

When I save a node I get the following error:

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'WHERE nid = 74' at line 3 query: UPDATE xmlsitemap_node SET pid = 354, previously_changed = last_changed, priority_override = WHERE nid = 74 in /home/kraquen/drupal/includes/database.mysql.inc on line 172.

it looks to me that "priority_override =" should be "priority_override = null" or something like that..

Thanks!