code: public CategorySeries addSeries(
        String seriesName,
        List<?> xData,
        List<? extends Number> yData,
        List<? extends Number> errorBars) {
  
      // Sanity checks
      sanityCheck(seriesName, xData, yData, errorBars);
  
      CategorySeries series;
      if (xData != null) {
  
        // Sanity check
        if (xData.size() != yData.size()) {
          throw new IllegalArgumentException("X and Y-Axis sizes are not the same!!!");
        }
  
        series = new CategorySeries(seriesName, xData, yData, errorBars, getDataType(xData));
      } else { // generate xData
        xData = Utils.getGeneratedDataAsList(yData.size());
        series = new CategorySeries(seriesName, xData, yData, errorBars, getDataType(xData));
      }
  
      seriesMap.put(seriesName, series);
  
      return series;
    }
docs: Add a series for a Category type chart using Lists with error bars
  
  @param seriesName
  @param xData the X-Axis data
  @param yData the Y-Axis data
  @param errorBars the error bar data
  @return A Series object that you can set properties on