protected static boolean hasFMUCElement( @Nonnull Packet stanza ) {
            return stanza.getElement().element(FMUC) != null;
        }
Represents a callback waiting for a stanza to be echo'd back from a remote FMUC node.
xmppserver/src/main/java/org/jivesoftware/openfire/muc/spi/FMUCHandler.java