@Override
    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
        type = (Type) ExternalizableUtil.getInstance().readSerializable(in);
        roomJID = new JID(ExternalizableUtil.getInstance().readSafeUTF(in), false);
        maxNumber = ExternalizableUtil.getInstance().readInt(in);

        if (ExternalizableUtil.getInstance().readBoolean(in)) {
            parent = (HistoryStrategy) ExternalizableUtil.getInstance().readSerializable(in);
        } else {
            parent = null;
        }

        if (ExternalizableUtil.getInstance().readBoolean(in)) {
            roomSubject = new Message((DefaultElement) ExternalizableUtil.getInstance().readSerializable(in));
        } else {
            roomSubject = null;
        }

        if (ExternalizableUtil.getInstance().readBoolean(in)) {
            contextPrefix = ExternalizableUtil.getInstance().readSafeUTF(in);
        } else {
            contextPrefix = null;
        }

        if (ExternalizableUtil.getInstance().readBoolean(in)) {
            contextSubdomain = ExternalizableUtil.getInstance().readSafeUTF(in);
        } else {
            contextSubdomain = null;
        }
    }
Removes all history that is maintained for this instance.
xmppserver/src/main/java/org/jivesoftware/openfire/muc/HistoryStrategy.java