Can’t Serialize JFreeChart Chart?

I was getting a serialization exception when I tried to serialize a JFreeChart chart to a file. The error message and corresponding stacktrace offered little in the way of clues. I finally figured out that the problem was with an interface implementation I had set for generating custom legend item labels. I used a lambda expression to supply the interface (XYSeriesLabelGenerator) implementation. Alternatively, one might use an anonymous inner class to provide the implementation. Neither of these approaches will work, as it is not possible (as far as I know) to implement the Serializable interface for the implementation. So, I used the good, old, named top-level class:

Source Code for CustomSeriesLabelGenerator

XYItemRenderer renderer = ...;
renderer.setLegendItemLabelGenerator(
        new CustomSeriesLabelGenerator());

So, if you are getting an error when serializing a JFreeChart chart, check how you have passed any interface implementations into a setter… that may be the problem.