}
        return null;
    }

    /**
     * Extracts URLs from HTML tag attributes using XPath.
     *
     * @param url the base URL for resolving relative URLs
     * @param document the document to extract URLs from
     * @param xpath the XPath expression to select elements
     * @param attr the attribute name to extract URLs from

                    name = values[values.length - 1];
                }
            }
        }

        /**
         * Normalizes the URL string by cleaning up multiple slashes and resolving relative paths.
         * This method ensures the URL is in a consistent format for FTP operations.
         *
         * @param s The URL string to normalize
         * @return The normalized URL string
         */