public function getTransactionHashes(
        int $blockCount,
        int $firstBlockIndex = null,
        string $blockHash = null,
        array $addresses = null,
        string $paymentId = null
    ):JsonResponse {
        $params = [
            'blockCount' => $blockCount,
        ];

        if (!is_null($firstBlockIndex)) $params['firstBlockIndex'] = $firstBlockIndex;
        if (!is_null($blockHash)) $params['blockHash'] = $blockHash;
        if (!is_null($addresses)) $params['addresses'] = $addresses;
        if (!is_null($paymentId)) $params['paymentId'] = $paymentId;

        return $this->rpcPost('getTransactionHashes', $params);
    }