code: private static void addAlgorithm(PMML pmml, Algorithm algorithm) {
          Extension extension = new Extension();
          extension.withName(ALGORITHM_EXTENSION_ELEMENT);
          extension.withValue(algorithm.name());
  
          pmml.withExtensions(extension);
      }
docs: Adds a {@link org.dmg.pmml.Extension} element to the {@link org.dmg.pmml.PMML} with the
  algorithm used to build the classifier.
  <p/>
  The name of the extension is {@link com.feedzai.fos.impl.weka.utils.pmml.PMMLConversionCommons#ALGORITHM_EXTENSION_ELEMENT}.
  
  @param pmml      The {@link PMML} to which add the algorithm.
  @param algorithm The algorithm used to build the classifier.