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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def committee_object(self):
        '''If the committee id no longer exists in mongo for some reason,
        this function returns None.
        '''
        if 'committee_id' in self:
            _id = self['committee_id']
            return self.document._old_roles_committees.get(_id)
        else:
            return self