code: public Observable<List<EntityExtractor>> listCustomPrebuiltEntitiesAsync(UUID appId, String versionId) {
          return listCustomPrebuiltEntitiesWithServiceResponseAsync(appId, versionId).map(new Func1<ServiceResponse<List<EntityExtractor>>, List<EntityExtractor>>() {
              @Override
              public List<EntityExtractor> call(ServiceResponse<List<EntityExtractor>> response) {
                  return response.body();
              }
          });
      }
docs: Gets all custom prebuilt entities information of this application.
  
  @param appId The application ID.
  @param versionId The version ID.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the List&lt;EntityExtractor&gt; object