public static function is_spam( array $values = [] ){
		$query_string = self::make_request( $values );
		// If Akismet is not active, always return error
		if( !class_exists('Akismet') || ! \Akismet::get_api_key() ){
			return new \WP_Error(500, 'Akismet is not active.');
		}
		// Make request
		add_filter('akismet_ua', [static::class, 'get_ua'], 9);
		$response = \Akismet::http_post($query_string, 'comment-check');
		remove_filter('akismet_ua', [static::class, 'get_ua'], 9);
		// Parse result
		switch( $response[1] ){
			case 'true':
				return true; // This is spam.
				break;
			case 'false':
				return false; // This is not spam.
				break;
			default:
				// Something is wrong
				if( isset( $response[0]['x-akismet-debug-help'] ) && !empty($response[0]['x-akismet-debug-help']) ){
					$message = $response[0]['x-akismet-debug-help'];
				}else{
					$message = 'Akismet return the invalid result. Something is wrong.';
				}
				return new \WP_Error(500, $message);
				break;
		}
	}