code: public static void addValue(String key, Object value, MultiValueMap<String, String> params) {
          if (value != null) {
              params.add(key, value.toString());
          }
      }
docs: Adds a param value to a params map. If value is null, nothing is done.
  
  @param key    the param key
  @param value  the param value
  @param params the params map