@Override
    public void writeExternal(ObjectOutput out) throws IOException
    {
		ExternalizableUtil.getInstance().writeBoolean( out, uniqueIdentifier != null);
		if ( uniqueIdentifier != null )
		{
			ExternalizableUtil.getInstance().writeSerializable( out, uniqueIdentifier );
		}
    }
Instantiates a flush task for a system-wide flush of pending changes.
xmppserver/src/main/java/org/jivesoftware/openfire/pubsub/cluster/FlushTask.java