Bug 127861 [DataBinding] Mark API provisional
bundles/org.eclipse.jface.databinding/src/org/eclipse/jface/databinding/viewers/UpdatableTreeContentProvider.java
public final Collection getChildren() {
            if (model == null) {
                return Collections.EMPTY_SET;
            }
            return model.toCollection();
        }
        
        /**
         * Called when this node is expanded
         */
        public void expanded() {
            for (Iterator iter = getChildren().iterator(); iter.hasNext();) {
                Object next = (Object) iter.next();
                ValueTreeNode childProvider = (ValueTreeNode) mapElementToValueTreeNode.get(next);
                childProvider.startListening();
            }
        }
        /**
         * Instructs this node to start monitoring child nodes
         */
        public void startListening() {
            if (model == null) {
                model = treeProvider.createChildList(node);
                if (model == null) {
                    model = EmptyReadableSet.getInstance();
                }
                model.addChangeListener(this);
                if (!childrenAddedToViewer) {
                	childrenAddedToViewer = true;
                	doAdd(model.toCollection());