code: public static void setParamDefault(
              final Multimap<String, String> params, final String key, final String value) {
          if (!params.containsKey(key)) {
              params.put(key, value);
          }
      }
docs: Add a parameter to the query params (the params map) if there is not existing value for that key.
  
  @param params the query parameters
  @param key the key/param name
  @param value the value to insert