code: public GroupResult group(List<UUID> faceIds) {
          return groupWithServiceResponseAsync(faceIds).toBlocking().single().body();
      }
docs: Divide candidate faces into groups based on face similarity.
  
  @param faceIds Array of candidate faceId created by Face - Detect. The maximum is 1000 faces
  @throws IllegalArgumentException thrown if parameters fail the validation
  @throws APIErrorException thrown if the request is rejected by server
  @throws RuntimeException all other wrapped checked exceptions if the request fails to be sent
  @return the GroupResult object if successful.