void addChildNode(Node child) {
        Log.trace("Add child node: {}", child.getNodeID());
        nodes.put(child.getUniqueIdentifier(), child);
    }
Adds a child node to the list of child nodes. The new child node may just have been
created or just restored from the database. This method will not trigger notifications
to node subscribers since the node could be a node that has just been loaded from the
database.

@param child the node to add to the list of child nodes.
xmppserver/src/main/java/org/jivesoftware/openfire/pubsub/CollectionNode.java