docs: @BetaApi
    public final ListInstancesRegionInstanceGroupsPagedResponse listInstancesRegionInstanceGroups(
        ProjectRegionInstanceGroupName instanceGroup,
        RegionInstanceGroupsListInstancesRequest regionInstanceGroupsListInstancesRequestResource) {
      ListInstancesRegionInstanceGroupsHttpRequest request =
          ListInstancesRegionInstanceGroupsHttpRequest.newBuilder()
              .setInstanceGroup(instanceGroup == null ? null : instanceGroup.toString())
              .setRegionInstanceGroupsListInstancesRequestResource(
                  regionInstanceGroupsListInstancesRequestResource)
              .build();
      return listInstancesRegionInstanceGroups(request);
    }