code: <T extends INode> T addChild(final T node, boolean inheritPermission) {
      return addChild(node, inheritPermission, true, UNKNOWN_INDEX);
    }
docs: Add a child inode to the directory.
  
  @param node INode to insert
  @param inheritPermission inherit permission from parent?
  @return  null if the child with this name already exists;
  node, otherwise