In Fuse 6.x, JavaMail fails to send an attachment with an empty message body

Issue

An application running on JBoss Fuse 6.x attempts to create an outbound mail message with an attachment but no message body, using the JavaMail API. The JavaMail operation fails with the following exception:

java.io.IOException: javax.mail.MessagingException: Empty multipart: multipart/related; 
    boundary="----=_Part_1_1764158333.1411422992098"
    at com.sun.mail.handlers.multipart_mixed.writeTo(multipart_mixed.java:105)
    at javax.activation.DataHandler.writeTo(DataHandler.java:77)
    at javax.mail.internet.MimeBodyPart.writeTo(MimeBodyPart.java:1485)
    at javax.mail.internet.MimeBodyPart.writeTo(MimeBodyPart.j

The same operation succeeds in a stand-alone Java application.