public function unregisterFileSystem($id)
    {
        $adapters = $this->getOption(self::OPTION_ADAPTERS);
        if (isset($adapters[$id])) {
            unset($adapters[$id]);
            if (isset($this->filesystems[$id])) {
                unset($this->filesystems[$id]);
            }
            $this->setOption(self::OPTION_ADAPTERS, $adapters);
            return true;
        } else {
            return false;
        }
    }