protected function getClient($clientName)
    {
        $clientName = $clientName ?: 'gbprod.elastica_extra.default_client';

        $client = $this->getContainer()
            ->get(
                $clientName,
                ContainerInterface::NULL_ON_INVALID_REFERENCE
            )
        ;

        $this->validateClient($client, $clientName);

        return $client;
    }