code: public List<ServerMonitoringStatistics> getMonitoringStats(Group group, ServerMonitoringFilter config) {
          checkNotNull(config, "Config must be not a null");
          return client.getMonitoringStatistics(
              idByRef(group),
              converter.createMonitoringStatisticRequest(config));
      }
docs: Retrieve the resource usage of servers within a group hierarchy statistics.
  @param group  Group reference
  @param config configuration for statistics entries
  @return the statistics list