Got this exception a few times. This was in a Swing-based app with a JFXPanel:

java.lang.NullPointerException
at com.sun.javafx.sg.BaseCacheFilter.render(BaseCacheFilter.java:226)
at com.sun.javafx.sg.prism.NGNode$CacheFilter.render(NGNode.java:769)
at com.sun.javafx.sg.prism.NGNode.renderCached(NGNode.java:710)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:422)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:69)
at com.sun.javafx.sg.BaseNode.render(BaseNode.java:1277)
at com.sun.javafx.sg.prism.NGGroup.renderChildren(NGGroup.java:242)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:208)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:1235)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:428)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:69)
at com.sun.javafx.sg.BaseNode.render(BaseNode.java:1277)
at com.sun.javafx.sg.prism.NGGroup.renderChildren(NGGroup.java:242)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:208)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:1235)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:428)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:69)
at com.sun.javafx.sg.BaseNode.render(BaseNode.java:1277)
at com.sun.javafx.sg.prism.NGGroup.renderChildren(NGGroup.java:242)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:208)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:1235)
at com.sun.javafx.sg.prism.NGNode.renderForClip(NGNode.java:649)
at com.sun.javafx.sg.prism.NGNode.renderRectClip(NGNode.java:543)
at com.sun.javafx.sg.prism.NGNode.renderClip(NGNode.java:569)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:424)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:69)
at com.sun.javafx.sg.BaseNode.render(BaseNode.java:1277)
at com.sun.javafx.sg.prism.NGGroup.renderChildren(NGGroup.java:242)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:208)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:1235)
at com.sun.javafx.sg.prism.NGNode.renderForClip(NGNode.java:649)
at com.sun.javafx.sg.prism.NGNode.renderRectClip(NGNode.java:543)
at com.sun.javafx.sg.prism.NGNode.renderClip(NGNode.java:569)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:424)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:69)
at com.sun.javafx.sg.BaseNode.render(BaseNode.java:1277)
at com.sun.javafx.sg.prism.NGGroup.renderChildren(NGGroup.java:242)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:208)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:1235)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:428)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:69)
at com.sun.javafx.sg.BaseNode.render(BaseNode.java:1277)
at com.sun.javafx.sg.prism.NGGroup.renderChildren(NGGroup.java:242)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:208)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:1235)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:428)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:69)
at com.sun.javafx.sg.BaseNode.render(BaseNode.java:1277)
at com.sun.javafx.sg.prism.NGGroup.renderChildren(NGGroup.java:242)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:208)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:1235)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:428)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:69)
at com.sun.javafx.sg.BaseNode.render(BaseNode.java:1277)
at com.sun.javafx.sg.prism.NGGroup.renderChildren(NGGroup.java:242)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:208)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:1235)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:428)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:69)
at com.sun.javafx.sg.BaseNode.render(BaseNode.java:1277)
at com.sun.javafx.sg.prism.NGGroup.renderChildren(NGGroup.java:242)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:208)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:1235)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:428)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:69)
at com.sun.javafx.sg.BaseNode.render(BaseNode.java:1277)
at com.sun.javafx.sg.prism.NGGroup.renderChildren(NGGroup.java:242)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:208)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:1235)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:428)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:69)
at com.sun.javafx.sg.BaseNode.render(BaseNode.java:1277)
at com.sun.javafx.sg.prism.NGGroup.renderChildren(NGGroup.java:242)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:208)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:1235)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:428)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:69)
at com.sun.javafx.sg.BaseNode.render(BaseNode.java:1277)
at com.sun.javafx.sg.prism.NGGroup.renderChildren(NGGroup.java:242)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:208)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:1235)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:428)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:69)
at com.sun.javafx.sg.BaseNode.render(BaseNode.java:1277)
at com.sun.javafx.tk.quantum.EmbeddedPainter.doPaint(EmbeddedPainter.java:132)
at com.sun.javafx.tk.quantum.AbstractPainter.paintImpl(AbstractPainter.java:213)
at com.sun.javafx.tk.quantum.EmbeddedPainter.run(EmbeddedPainter.java:107)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:304)
at com.sun.prism.render.RenderJob.run(RenderJob.java:56)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at com.sun.javafx.tk.quantum.QuantumRenderer$PipelineRunnable.run(QuantumRenderer.java:131)
at java.lang.Thread.run(Thread.java:722)