public function clear($cache = null)
    {
        if ($cache === null) {
            $cache = $this->cache_name;
        }
        $cache = self::encodeCache($cache);
        $url = "projects/{$this->project_id}/caches/$cache/clear";
        $params = array();
        $this->setJsonHeaders();
        return self::json_decode($this->apiCall(self::POST, $url, $params));
    }