* URLs using these rules.</p>
 *
 * <p>The conversion is performed by iterating through the conversion map and applying
 * each replacement rule sequentially. The order of the rules in the map is preserved
 * during the conversion process.</p>
 *
 * <p>Example usage:</p>
 *
 * <pre>{@code
 * UrlConvertHelper helper = new UrlConvertHelper();
 * helper.add("old-domain.com", "new-domain.com");