* @return node or <code>null</code>
*/
public AbstractNodeData retrieveFirst(NodeId id) {
ReferenceMap map = (ReferenceMap) cache.get(id);
if (map != null) {
Iterator iter = map.values().iterator();
try {
while (iter.hasNext()) {
AbstractNodeData data = (AbstractNodeData) iter.next();
if (data != null) {
return data;