code: public boolean addGroupEntities(String entityGroupName, Boolean createEntities, Entity... entities) {
          checkEntityGroupIsEmpty(entityGroupName);
          List<String> entitiesNames = new ArrayList<>();
          for (Entity entity : entities) {
              entitiesNames.add(entity.getName());
          }
          QueryPart<EntityGroup> query = new Query<EntityGroup>("entity-groups")
                  .path(entityGroupName, true)
                  .path("entities/add")
                  .param("createEntities", createEntities);
          return httpClientManager.updateData(query, post(entitiesNames));
      }
docs: Add specified entities to entity group.
  
  @param entityGroupName Entity group name.
  @param createEntities  Automatically create new entities from the submitted list if such entities don't already exist.
  @param entities        Entities to create.
  @return {@code true} if entities added.
  @throws AtsdClientException raised if there is any client problem
  @throws AtsdServerException raised if there is any server problem