code: protected void addSubTitle(JFreeChart chart, String subTitle, Font font)
  	{
  		if (StringUtils.isNotEmpty(subTitle))
  		{
  			TextTitle chartSubTitle = new TextTitle(subTitle);
  			customizeTitle(chartSubTitle, font);
  			chart.addSubtitle(chartSubTitle);
  		}
  	}
docs: <p>addSubTitle.</p>
  
  @param chart a {@link org.jfree.chart.JFreeChart} object.
  @param subTitle a {@link java.lang.String} object.
  @param font a {@link java.awt.Font} object.