code: public ModifyInstanceGroupsRequest withInstanceGroup(ModifyInstanceGroupConfig instanceGroup) {
          if (this.instanceGroups == null) {
              this.instanceGroups = new ArrayList<ModifyInstanceGroupConfig>();
          }
          this.instanceGroups.add(instanceGroup);
          return this;
      }
docs: Configure the instance group to be modified.
  
  @param instanceGroup an instance group config to be added.
  @return ModifyInstanceGroupsRequest