[trunk] : Error when Reset to Unconfirmed Meeting

When Click on Reset to Unconfirmed Meeting error occurred following trace back

Traceback:
    eturn f(self, dbname, *args, **kwargs)
  File "/home/dbr/workspace/source/server/trunk/openerp/osv/osv.py", line 174, in execute
    res = self.execute_cr(cr, uid, obj, method, *args, **kw)
  File "/home/dbr/workspace/source/server/trunk/openerp/osv/osv.py", line 165, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "/home/dbr/workspace/source/addons/trunk/crm/crm.py", line 239, in case_reset
    self._history(cr, uid, cases, _('Draft'))
AttributeError: 'crm.meeting' object has no attribute '_history'