code: public OperationFuture<Group> modify(Group groupRef, GroupConfig groupConfig) {
          checkNotNull(groupConfig, "GroupConfig must be not null");
          checkNotNull(groupRef, "Group reference must be not null");
          updateGroup(idByRef(groupRef), groupConfig);
  
          return new OperationFuture<>(
              groupRef,
              new NoWaitingJobFuture()
          );
      }
docs: Update group
  @param groupRef    group reference
  @param groupConfig group config
  @return OperationFuture wrapper for Group