code: @Nullable
    public AlluxioURI getParent() {
      String path = mUri.getPath();
      int lastSlash = path.lastIndexOf('/');
      int start = hasWindowsDrive(path, true) ? 3 : 0;
      if ((path.length() == start) || // empty path
          (lastSlash == start && path.length() == start + 1)) { // at root
        return null;
      }
      String parent;
      if (lastSlash == -1) {
        parent = CUR_DIR;
      } else {
        int end = hasWindowsDrive(path, true) ? 3 : 0;
        parent = path.substring(0, lastSlash == end ? end + 1 : lastSlash);
      }
      return new AlluxioURI(this, parent, false);
    }
docs: Get the parent of this {@link AlluxioURI} or null if at root.
  
  @return the parent of this {@link AlluxioURI} or null if at root