public function create_directory($newdirname, $userid = NULL) {
        if (!$this->is_writable() or !$this->lf->is_directory()) {
            return null;
        }

        $newdirname = clean_param($newdirname, PARAM_FILE);
        if ($newdirname === '') {
            return null;
        }

        $filepath = $this->lf->get_filepath().'/'.$newdirname.'/';

        $fs = get_file_storage();

        if ($file = $fs->create_directory($this->lf->get_contextid(), $this->lf->get_component(), $this->lf->get_filearea(), $this->lf->get_itemid(), $filepath, $userid)) {
            return $this->browser->get_file_info($this->context, $this->lf->get_component(), $file->get_filearea(), $file->get_itemid(), $file->get_filepath(), $file->get_filename());
        }
        return null;
    }