public function getWaiters()
    {
        if (!isset($this->waiters)) {
            $res = call_user_func(
                $this->apiProvider,
                'waiter',
                $this->serviceName,
                $this->apiVersion
            );
            $this->waiters = isset($res['waiters'])
                ? $res['waiters']
                : [];
        }

        return $this->waiters;
    }