Null pointer exception

[saranyaelumalai-okta]

Hi,
My public private key pair was created using openssl command. When tried to sign the message using java-utils-mail-dkim library, it throws Null Pointer exception at DkimMessage.getBytes . Please guide on whats causing this issue.

Here is the complete stack trace.

java.lang.NullPointerException: null
	at com.saasure.core.services.mail.eemsg.util.DkimMessage.getBytes(DkimMessage.java:150)
	at com.saasure.core.services.mail.eemsg.util.DkimMessage.writeln(DkimMessage.java:144)
	at com.saasure.core.services.mail.eemsg.util.DkimMessage.writeTo(DkimMessage.java:109)
	at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:1315)
	at com.saasure.core.services.mail.impl.EmailSenderImpl.send(EmailSenderImpl.java:345)

Here is how, I used it

....
MimeMessage dkimSignedMessage = dkimSignMessage (mimeMessage, domain, selector, privateKey);
t.sendMessage(dkimSignedMessage, uniqueRecipients);
.....
.....

    private MimeMessage dkimSignMessage(MimeMessage message,  String signingDomain, String selector,  String privateKey)  throws Exception {
        DkimSigner dkimSigner = new DkimSigner(signingDomain, selector, privateKey );
        dkimSigner.setHeaderCanonicalization(Canonicalization.SIMPLE);
        dkimSigner.setBodyCanonicalization(Canonicalization.RELAXED);
        dkimSigner.setSigningAlgorithm(SigningAlgorithm.SHA256_WITH_RSA);
        dkimSigner.setLengthParam(true);
        dkimSigner.setCopyHeaderFields(false);
        return new DkimMessage(message, dkimSigner);
    }