SetBody DSL should remove specialized Message as its no long apply

Also an issue from
http://old.nabble.com/Original-message-body-lost-in-transacted-route-to26451809.html

This issue is because the JmsMessage is still set as the IN message object and it contain the backing javax.jms.Message object. So when you for example use the setBody DSL to set a {{null} body or empty body then it may fallback and look into the specialized JmsMessage object.

Set SetBodyProcessor should set a new DefaultMessage with the headers propagated and the new body evaluated.