try (FileSystem fs = Jimfs.newFileSystem(Configuration.unix())) {
      Path root = fs.getRootDirectories().iterator().next();
      assertNull(root.getParent());
      assertNull(root.toRealPath().getParent());
      MoreFiles.createParentDirectories(root); // test that there's no exception
    }
  }

  public void testCreateParentDirectories_relativePath() throws IOException {