Guys, Which module need to be added as a depended to have "Chatter" available in custom module ?

I just added "Mail" as a 'depended' in __openerp__.py and 'inherit = "mail.thread" '

but apparently its not enough ....

Getting error:

if not obj.user_id or not obj.user_id.partner_id:

AttributeError: 'unicode' object has no attribute 'partner_id'

What should I add to have this functionality available in custom module ?