private function getContactIdentifier(Identity $orderIdentity)
    {
        $order = $this->client->request('GET', 'orders/' . $orderIdentity->getAdapterIdentifier());

        $relations = array_filter($order['relations'], function (array $relation) {
            return $relation['referenceType'] === 'contact';
        });

        if (empty($relations)) {
            return null;
        }

        $contactRelation = array_shift($relations);

        return $contactRelation['referenceId'];
    }
private function getContactIdentifier(Identity $orderIdentity)
    {
        $order = $this->client->request('GET', 'orders/' . $orderIdentity->getAdapterIdentifier());

        $relations = array_filter($order['relations'], function (array $relation) {
            return $relation['referenceType'] === 'contact';
        });

        if (empty($relations)) {
            return null;
        }

        $contactRelation = array_shift($relations);

        return $contactRelation['referenceId'];
    }
@param Identity $orderIdentity

@return null|int