public function update($identity, $label = null, $master = null, $status = null)
    {

        $params = array();
        if (! is_null($label)) {
            $params['label'] = $label;
        }
        if (! is_null($master)) {
            $params['master'] = $master;
        }
        if (! is_null($status)) {
            $params['status'] = $status;
        }

        return $this->_user->put('account/identity/' . $identity, $params);
    }