@Override
    public void printStackTrace() {
        super.printStackTrace();
        if (nestedThrowable != null) {
            nestedThrowable.printStackTrace();
        }
    }
Exception used for representing unavailability of FMUC (XEP-0289). The resulting error is expected to be delivered
to the originating entity in the form of a presence stanza, possibly containing a human-readable 'reject' message.

@author Guus der Kinderen, guus@goodbytes.nl
@see <a href="https://xmpp.org/extensions/xep-0289.html">XEP-0289: Federated MUC for Constrained Environments</a>
xmppserver/src/main/java/org/jivesoftware/openfire/muc/FMUCException.java