code: public Map<Group, List<ServerMonitoringStatistics>> getMonitoringStatsAsMap(GroupFilter groupFilter, ServerMonitoringFilter config) {
          return getMonitoringStatsAsMap(Arrays.asList(getRefsFromFilter(groupFilter)), config);
      }
docs: Retrieve the resource usage of servers within a group hierarchy statistics.
  @param groupFilter group filter
  @param config      configuration for statistics entries
  @return the statistics map