docs: public @Nullable String build() {
      StringBuilder queryString = new StringBuilder();
  
      for (NameValuePair param : params) {
        if (queryString.length() > 0) {
          queryString.append(PARAM_SEPARATOR);
        }
        queryString.append(Escape.urlEncode(param.getName()));
        queryString.append(VALUE_SEPARATOR);
        queryString.append(Escape.urlEncode(param.getValue()));
      }
  
      if (queryString.length() > 0) {
        return queryString.toString();
      }
      else {
        return null;
      }
    }