protected function load()
    {
        $json = file_get_contents($this->filename);
        if (false === $json) {
            // @codeCoverageIgnoreStart
            throw new RuntimeException('Unable to open file ' . $this->filename);
            // @codeCoverageIgnoreEnd
        }

        $this->unserialize($json);
        $this->cookies = $this->cookies ?: array();
    }