docs: public void refresh(String index) throws IOException {
          logger.debug("refresh index [{}]", index);
  
          String path = "/";
  
          if (index != null) {
              path += index + "/";
          }
  
          path += "_refresh";
  
          Response restResponse = lowLevelClient.performRequest("POST", path);
          logger.trace("refresh raw response: {}", asMap(restResponse));
      }