@Override
    public void writeExternal(ObjectOutput out) throws IOException {
        ExternalizableUtil.getInstance().writeSerializable(out, type);
        ExternalizableUtil.getInstance().writeSafeUTF(out, roomJID.toString());
        ExternalizableUtil.getInstance().writeInt(out, maxNumber);

        ExternalizableUtil.getInstance().writeBoolean(out,parent != null);
        if (parent != null) {
            ExternalizableUtil.getInstance().writeSerializable(out, parent);
        }

        ExternalizableUtil.getInstance().writeBoolean(out, roomSubject != null);
        if (roomSubject != null) {
            ExternalizableUtil.getInstance().writeSerializable(out, (DefaultElement)roomSubject.getElement());
        }

        ExternalizableUtil.getInstance().writeBoolean(out, contextPrefix != null);
        if (contextPrefix != null) {
            ExternalizableUtil.getInstance().writeSafeUTF(out, contextPrefix);
        }

        ExternalizableUtil.getInstance().writeBoolean(out, contextSubdomain != null);
        if (contextSubdomain != null) {
            ExternalizableUtil.getInstance().writeSafeUTF(out, contextSubdomain);
        }
    }
Removes all history that is maintained for this instance.
xmppserver/src/main/java/org/jivesoftware/openfire/muc/HistoryStrategy.java