docs: protected int addOriginalDocument(String text, int label)
      {
          if(label >= labelInfo.getNumOfCategories())
              throw new RuntimeException("Invalid label given");
          int index = super.addOriginalDocument(text);
          synchronized(classLabels)
          {
              while(classLabels.size() < index)
                  classLabels.add(-1);
              if(classLabels.size() ==  index)//we are where we expect
                  classLabels.add(label);
              else//another thread beat us to the addition
                  classLabels.set(index, label);
          }
          return index;
      }