I have code that is accidentally passing NaN values to the 1st, 3rd, and 4th double values for the 6 parameter constructor of XYLineAnnotation(). See: https://github.com/jfree/jfreechart/blob/master/src/main/java/org/jfree/chart/annotations/XYLineAnnotation.java#L118

This annotation is then added to a chart, and later on, when I invoke ChartUtils.writeChartAsPNG() with this chart, that method simply hangs. Seems like the XYLineAnnotation() constructors should all verify that all the doubles passed to them are actual numbers. Regardless, the ChartUtils.writeChartAsPNG() method shouldn't simply hang.