messageGatewayService : NPE

Hi, I am getting NPE when calling EmailService class's function sendEmail(). @Component(immediate = true, metatype = true, label = "Mail Service") @Service(EmailService.class) public class EmailService { @Reference private MessageGateway<HtmlEmail> messageGateway; @Reference private MessageGatewayService messageGatewayService; public void sendEmail() { ArrayList<InternetAddress> emailRecipients = new ArrayList<InternetAddress>(); HtmlEmail email = new HtmlEmail(); try { emailRecipients.add(new InternetAddress("recipient.gmail.com")); email.setTo(emailRecipients); email.setSubject("This is subject"); email.setHtmlMsg("Email testing is on.."); logger.info("messageGatewayService : " + messageGatewayService); messageGateway = messageGatewayService.getGateway(HtmlEmail.class); // Check the logs to see that messageGateway is not null logger.info("messageGateway : " + messageGateway); messageGateway.send(email); } //Catch Block }