#channel_id.message_post(body=body,
                        #subject=title,
                        #subtype_xmlid='mail.box_inbox',
                        #author_id=self.env.user.partner_id.id,
                        #attachment_ids=[attachment.id],)
from this code i am sending the ir.attachment(514,) object . but the message is a blank image or blank pdf .
 
am i missing something? 
