问通过Openerp 7“社交网络”应用程序发送附件时出错，但在发送正常消息时运行良好

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Client Traceback (most recent call last):
  File "/usr/lib/pymodules/python2.7/openerp/addons/web/http.py", line 204, in dispatch
    response["result"] = method(self, **self.params)
  File "/usr/lib/pymodules/python2.7/openerp/addons/web/controllers/main.py", line 1125, in call_button
    action = self._call_kw(req, model, method, args, {})
  File "/usr/lib/pymodules/python2.7/openerp/addons/web/controllers/main.py", line 1113, in _call_kw
    return getattr(req.session.model(model), method)(*args, **kwargs)
  File "/usr/lib/pymodules/python2.7/openerp/addons/web/session.py", line 42, in proxy
    result = self.proxy.execute_kw(self.session._db, self.session._uid, self.session._password, self.model, method, args, kw)
  File "/usr/lib/pymodules/python2.7/openerp/addons/web/session.py", line 30, in proxy_method
    result = self.session.send(self.service_name, method, *args)
  File "/usr/lib/pymodules/python2.7/openerp/addons/web/session.py", line 103, in send
    raise xmlrpclib.Fault(openerp.tools.ustr(e), formatted_info)


Server Traceback (most recent call last):
  File "/usr/lib/pymodules/python2.7/openerp/addons/web/session.py", line 89, in send
    return openerp.netsvc.dispatch_rpc(service_name, method, args)
  File "/usr/lib/pymodules/python2.7/openerp/netsvc.py", line 292, in dispatch_rpc
    result = ExportService.getService(service_name).dispatch(method, params)
  File "/usr/lib/pymodules/python2.7/openerp/service/web_services.py", line 626, in dispatch
    res = fn(db, uid, *params)
  File "/usr/lib/pymodules/python2.7/openerp/osv/osv.py", line 188, in execute_kw
    return self.execute(db, uid, obj, method, *args, **kw or {})
  File "/usr/lib/pymodules/python2.7/openerp/osv/osv.py", line 131, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "/usr/lib/pymodules/python2.7/openerp/osv/osv.py", line 197, in execute
    res = self.execute_cr(cr, uid, obj, method, *args, **kw)
  File "/usr/lib/pymodules/python2.7/openerp/osv/osv.py", line 185, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "/usr/lib/pymodules/python2.7/openerp/addons/purchase/purchase.py", line 1223, in send_mail
    return super(mail_compose_message, self).send_mail(cr, uid, ids, context=context)
  File "/usr/lib/pymodules/python2.7/openerp/addons/sale/sale.py", line 996, in send_mail
    return super(mail_compose_message, self).send_mail(cr, uid, ids, context=context)
  File "/usr/lib/pymodules/python2.7/openerp/addons/account/account_invoice.py", line 1790, in send_mail
    return super(mail_compose_message, self).send_mail(cr, uid, ids, context=context)
  File "/usr/lib/pymodules/python2.7/openerp/addons/email_template/wizard/mail_compose_message.py", line 80, in send_mail
    return super(mail_compose_message, self).send_mail(cr, uid, ids, context=context)
  File "/usr/lib/pymodules/python2.7/openerp/addons/mail/wizard/mail_compose_message.py", line 259, in send_mail
    msg_id = active_model_pool.message_post(cr, uid, [res_id], type='comment', subtype=subtype, context=context, **post_values)
  File "/usr/lib/pymodules/python2.7/openerp/addons/mail/mail_thread.py", line 1052, in message_post
    ir_attachment.write(cr, SUPERUSER_ID, filtered_attachment_ids, {'res_model': model, 'res_id': thread_id}, context=context)
  File "/usr/lib/pymodules/python2.7/openerp/addons/base_calendar/crm_meeting.py", line 160, in write
    return super(ir_attachment, self).write(cr, uid, ids, vals, context=context)
  File "/usr/lib/pymodules/python2.7/openerp/addons/document/document.py", line 129, in write
    return super(document_file, self).write(cr, uid, ids, vals, context)
  File "/usr/lib/pymodules/python2.7/openerp/addons/base/ir/ir_attachment.py", line 268, in write
    self.check(cr, uid, ids, 'write', context=context, values=vals)
  File "/usr/lib/pymodules/python2.7/openerp/addons/document/document.py", line 76, in check
    return super(document_file, self).check(cr, uid, ids, mode='read', context=context, values=values)
  File "/usr/lib/pymodules/python2.7/openerp/addons/base/ir/ir_attachment.py", line 208, in check
    mids = self.pool.get(model).exists(cr, uid, mids)

AttributeError: 'NoneType' object has no attribute 'exists'