@Override
    public void printStackTrace() {
        super.printStackTrace();
        if (nestedThrowable != null) {
            nestedThrowable.printStackTrace();
        }
    }
Exception used for representing that the MultiUserChat service is not available at the moment.
There are many reasons why a ServiceUnavailableException could occur such as: a user is trying
to join a room that has reached the max number of occupants.

@author Gaston Dombiak
xmppserver/src/main/java/org/jivesoftware/openfire/muc/ServiceUnavailableException.java