code: public Observable<UUID> addHierarchicalEntityChildAsync(UUID appId, String versionId, UUID hEntityId, AddHierarchicalEntityChildOptionalParameter addHierarchicalEntityChildOptionalParameter) {
          return addHierarchicalEntityChildWithServiceResponseAsync(appId, versionId, hEntityId, addHierarchicalEntityChildOptionalParameter).map(new Func1<ServiceResponse<UUID>, UUID>() {
              @Override
              public UUID call(ServiceResponse<UUID> response) {
                  return response.body();
              }
          });
      }
docs: Creates a single child in an existing hierarchical entity model.
  
  @param appId The application ID.
  @param versionId The version ID.
  @param hEntityId The hierarchical entity extractor ID.
  @param addHierarchicalEntityChildOptionalParameter the object representing the optional parameters to be set before calling this API
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the UUID object