docs: public static INDArray asExampleMatrix(Window window, Word2Vec vec) {
          INDArray[] data = new INDArray[window.getWords().size()];
          for (int i = 0; i < data.length; i++) {
              data[i] = vec.getWordVectorMatrix(window.getWord(i));
  
              // if there's null elements
              if (data[i] == null)
                  data[i] = Nd4j.zeros(1, vec.getLayerSize());
          }
          return Nd4j.hstack(data);
      }