public boolean hasChildren(final ExplorerNode parent) {
        final K nodeKey = getNodeKey(parent);
        return NullSafe.hasItems(parentKeyToChildNodesMap.get(nodeKey));
    }
@param key
@return True if the node for this key has at least one child
stroom-explorer/stroom-explorer-impl/src/main/java/stroom/explorer/impl/AbstractTreeModel.java