public function sendData($data)
    {
        // Issue #20 no data values should be null.

        array_walk($data, function (&$value) {
            if (! isset($value)) {
                $value = '';
            }
        });

        $httpResponse = $this
            ->httpClient
            ->request(
                'POST',
                $this->getEndpoint(),
                [
                    'Content-Type' => 'application/x-www-form-urlencoded',
                ],
                http_build_query($data)
            );

        // We might want to check $httpResponse->getStatusCode()

        $responseData = static::parseBodyData($httpResponse);

        return $this->createResponse($responseData);
    }