@Nullable
  public TreeNode getNextChildByKey(final String key, final boolean isFolder) {
    final ByKeySelectedSearcher searcher = (isFolder) ? new FolderByKeySelectedSearcher(key, myChildren) :
                                                 new FileByKeySelectedSearcher(key, myChildren);
    return searcher.getNextSelectedByKey();
  }
@Nullable
  public TreeNode getNextChildByKey(final String key, final boolean isFolder)