public function addFile($key, $filepath, $mimeType = '')
    {
        $value = \base64_encode(\file_get_contents($filepath));

        if (!empty($mimeType)) {
            $value = ['_content_type' => $mimeType, '_name' => $filepath, '_content' => $value];
        }

        $this->set($key, $value);

        return $this;
    }