synchronized void addResponse( @Nonnull final Packet stanza ) {
            this.responses.add( stanza );
            if (joinResult == null) {
                if ( isSubject( stanza ) ) {
                    joinResult = true;
                }
                if ( isFMUCReject( stanza ) ) {
                    joinResult = false;
                }
            }
        }
The state of the federation join. Null means that the request is pending completion. True means a successful
join was achieved, while false means that the join request failed or was aborted.
xmppserver/src/main/java/org/jivesoftware/openfire/muc/spi/FMUCHandler.java