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