public PublishedItem getPublishedItem(String itemID) {
        return null;
    }
Returns the {@link PublishedItem} whose ID matches the specified item ID or {@code null}
if none was found. Item ID may or may not exist and it depends on the node's configuration.
When the node is configured to not include payloads in event notifications and
published items are not persistent then item ID is not used. In this case a {@code null}
value will always be returned.

@param itemID the ID of the item to retrieve.
@return the PublishedItem whose ID matches the specified item ID or null if none was found.
xmppserver/src/main/java/org/jivesoftware/openfire/pubsub/Node.java