/**
     * Validates if the given URL string is a valid URL.
     *
     * @param urlStr the URL string to validate
     * @return true if the URL is valid, false otherwise
     */
    protected boolean isValidUrl(final String urlStr) {
        if (StringUtil.isBlank(urlStr)) {
            return false;
        }
        final String value;
        if (urlStr.startsWith("://")) {
            value = "http" + urlStr;

        assertTrue(transformer.isValidUrl("http://www.example.com"));
        assertTrue(transformer.isValidUrl("http://www.example.com/aaa"));
        assertTrue(transformer.isValidUrl("https://www.example.com"));
        assertTrue(transformer.isValidUrl("://www.example.com"));
        assertTrue(transformer.isValidUrl("//www.example.com"));

        assertFalse(transformer.isValidUrl(null));