org.springframework.mail.MailSendException: Failed messages: java.lang.NullPointerException

spring.mail.default-encoding=UTF-8
spring.mail.protocol=smtp
spring.mail.host= smtp.gmail.com
spring.mail.username= myeamil@gmail.com
spring.mail.password= password
spring.mail.port= 587
spring.mail.properties.mail.smtp.starttls.enable= true
spring.mail.properties.mail.auth= true

@Autowired
    private JavaMailSender mailSender;

    private SimpleMailMessage simpleMailMessage=new SimpleMailMessage();

public ResponseDTO saveUser(UserDTO userDTO) {
            userRepositry.save(userDTO);
            simpleMailMessage.setFrom("myemail@gmail.com");
            simpleMailMessage.setSubject("some data");
            simpleMailMessage.setText("some data");
            mailSender.send(simpleMailMessage);
            simpleMailMessage.setTo(userDTO.getEmail());
            return new ResponseDTO("Registeration is done successfully..",true);

    }