For each user in any client， system create 8 preference values in system client using their ad_user_id.
When browsering these data in System Preference Window , the field of AD_USER_ID is null as Table Direct reference. The record is changed after navigating other records . The changlog show the ad_user_id set to null by system user.
I think users in all clients should allow system user to maintenant in this field/column, so i change it's reference to fix this issue.
Thanks for review my patch.