code: public OperationFuture<Group> create(GroupConfig groupConfig) {
          checkNotNull(groupConfig, "GroupConfig must be not null");
          checkNotNull(groupConfig.getName(), "Name of GroupConfig must be not null");
          checkNotNull(groupConfig.getParentGroup(), "ParentGroup of GroupConfig must be not null");
  
          GroupMetadata group = client.createGroup(
                  converter.createGroupRequest(groupConfig, idByRef(groupConfig.getParentGroup()),
                      groupConfig.getCustomFields() == null || groupConfig.getCustomFields().size() == 0 ?
                          null : client.getCustomFields()
                  ));
  
          return new OperationFuture<>(
              Group.refById(group.getId()),
              new NoWaitingJobFuture()
          );
      }
docs: Create group
  @param groupConfig group config
  @return OperationFuture wrapper for Group