public Set<ExplorerNode> getChildrenWithDescendantInfo(final ExplorerNode parent) {
        final K parentKey = getNodeKey(parent);
        return parentKeyToChildNodesMap.get(parentKey);
    }
@return The sub-set of childNodes that have node info or one of their descendants has it.
stroom-explorer/stroom-explorer-impl/src/main/java/stroom/explorer/impl/AbstractTreeModel.java