code: public void publishAdditionalModelData(JavaSparkContext sparkContext,
                                           PMML pmml,
                                           JavaRDD<M> newData,
                                           JavaRDD<M> pastData,
                                           Path modelParentPath,
                                           TopicProducer<String, String> modelUpdateTopic) {
      // Do nothing by default
    }
docs: Optionally, publish additional model-related information to the update topic,
  after the model has been written. This is needed only in specific cases, like the
  ALS algorithm, where the model serialization in PMML can't contain all of the info.
  
  @param sparkContext active Spark Context
  @param pmml model for which extra data should be written
  @param newData data that has arrived in current interval
  @param pastData all previously-known data (may be {@code null})
  @param modelParentPath directory containing model files, if applicable
  @param modelUpdateTopic message topic to write to