Missing function in transport file about magento2-mandrill HOT 5 CLOSED

<?php
/**
 * Ebizmarts_Mandrill Magento JS component
 *
 * @category    Ebizmarts
 * @package     Ebizmarts_Mandrill
 * @author      Ebizmarts Team <[email protected]>
 * @copyright   Ebizmarts (http://ebizmarts.com)
 * @license     http://opensource.org/licenses/osl-3.0.php  Open Software License (OSL 3.0)
 */

namespace Ebizmarts\Mandrill\Model;

class Transport implements \Magento\Framework\Mail\TransportInterface
{
    /**
     * @var \Ebizmarts\Mandrill\Model\Message
     */
    private $message;

    /**
     * @var Api\Mandrill
     */
    private $api;

    /**
     * @param \Magento\Framework\Mail\MessageInterface $message
     * @param \Psr\Log\LoggerInterface $logger
     * @param \Ebizmarts\Mandrill\Helper\Data $helper
     */
    public function __construct(
        \Ebizmarts\Mandrill\Model\Message $message,
        \Ebizmarts\Mandrill\Model\Api\Mandrill $api
    ) {
    
        $this->message = $message;
        $this->api     = $api;
    }
    public function sendMessage()
    {
        $mandrillApiInstance = $this->getMandrillApiInstance();

        if ($mandrillApiInstance === null) {
            return false;
        }

        $message    = array(
            'subject' => $this->message->getSubject(),
            'from_name' => $this->message->getFromName(),
            'from_email'=> $this->message->getFrom(),
        );
        foreach ($this->message->getTo() as $to) {
            $message['to'][] = array(
                'email' => $to
            );
        }
        foreach ($this->message->getBcc() as $bcc) {
            $message['to'][] = array(
                'email' => $bcc,
                'type' => 'bcc'
            );
        }
        if ($att = $this->message->getAttachments()) {
            $message['attachments'] = $att;
        }
        if ($headers = $this->message->getHeaders()) {
            $message['headers'] = $headers;
        }
        switch ($this->message->getType()) {
            case \Magento\Framework\Mail\MessageInterface::TYPE_HTML:
                $message['html'] = $this->message->getBody();
                break;
            case \Magento\Framework\Mail\MessageInterface::TYPE_TEXT:
                $message['text'] = $this->message->getBody();
                break;
        }

        $result = $mandrillApiInstance->messages->send($message);

        $this->processApiCallResult($result);

        return true;
    }

    private function processApiCallResult($result)
    {
        $currentResult = current($result);

        if (array_key_exists('status', $currentResult) && $currentResult['status'] == 'rejected') {
            throw new \Magento\Framework\Exception\MailException(
                new \Magento\Framework\Phrase("Email sending failed: %1", [$currentResult['reject_reason']])
            );
        }
    }

    /**
     * @return \Mandrill
     */
    private function getMandrillApiInstance()
    {
        return $this->api->getApi();
    }

    /**
     * Needed to be added otherwise during setup:di:compile you'll get an error.
     *
     * @return string
     */
    public function getMessage(){return;}
}