@Override
 public Node findNode(String nodeId) {
   try {
     return FileSystemNode.findNode(rootDirectory, nodeId);
   } catch (IOException e) {
     throw new StorageException(e);
   }
 }
 @Override
 public Node createNode(NodeBuilder builder) {
   try {
     return FileSystemNode.create(rootDirectory, idGenerator.createId(), builder);
   } catch (IOException e) {
     throw new StorageException(e);
   }
 }