NPE when sending plain text email

If I create just plain text view (.txt) for email, I get an NPE:
play.exceptions.JavaExecutionException
        at play.mvc.ActionInvoker.invoke(ActionInvoker.java:200)
        at Invocation.HTTP Request(Play!)
Caused by: java.lang.NullPointerException
        at javax.mail.internet.MimeUtility.checkAscii(MimeUtility.java:1346)
        at javax.mail.internet.MimeBodyPart.setText(MimeBodyPart.java:1069)
        at javax.mail.internet.MimeMessage.setText(MimeMessage.java:1493)
        at javax.mail.internet.MimeMessage.setText(MimeMessage.java:1477)
        at play.libs.Mail.buildMessage(Mail.java:215)
        at play.libs.Mail.send(Mail.java:162)
        at play.mvc.Mailer.send(Mailer.java:190)

It occurs because of this line in Mail.java:
        if ("text/plain".equals(contentType)) {
            msg.setText(body);
Variable 'body' is in this case null and the actual mail is in 'alternate' variable
I am using Play 1.0