public static String encodingParams(Map<String, String> params, String encoding)
            throws UnsupportedEncodingException {
        StringBuilder sb = new StringBuilder();
        if (null == params || params.isEmpty()) {
            return null;
        }
        for (Map.Entry<String, String> entry : params.entrySet()) {
            if (StringUtils.isEmpty(entry.getValue())) {
                continue;
            }
            
            sb.append(entry.getKey()).append('=');
            sb.append(URLEncoder.encode(entry.getValue(), encoding));
            sb.append('&');
        }
        
        return sb.toString();
    }
@Test
    void testEncodingParamsListWithNull() throws UnsupportedEncodingException {
        assertNull(HttpUtils.encodingParams((List<String>) null, "UTF-8"));
    }