NullPointerException when xchart panel width is too small

[landret]

Hi, I am using XChartPanel<XYChart> to display a chart using its paint() method. This panel is put in a frame. However, when the frame width becomes too small (for instance by using the mouse to decrease the frame width), a NullPointerException will occur repeateadly.

Here is the exception:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
	at org.knowm.xchart.internal.chartpart.PlotContent_XY.doPaint(PlotContent_XY.java:308)
	at org.knowm.xchart.internal.chartpart.PlotContent_.paint(PlotContent_.java:62)
	at org.knowm.xchart.internal.chartpart.Plot_.paint(Plot_.java:38)
	at org.knowm.xchart.internal.chartpart.Plot_AxesChart.paint(Plot_AxesChart.java:35)
	at org.knowm.xchart.XYChart.paint(XYChart.java:417)
	at org.knowm.xchart.XChartPanel.paintComponent(XChartPanel.java:168)
	at javax.swing.JComponent.paint(JComponent.java:1056)
	at javax.swing.JComponent.paintChildren(JComponent.java:889)
	at javax.swing.JComponent.paint(JComponent.java:1065)
	at javax.swing.JComponent.paintChildren(JComponent.java:889)
	at javax.swing.JComponent.paint(JComponent.java:1065)
	at javax.swing.JComponent.paintChildren(JComponent.java:889)
	at javax.swing.JComponent.paint(JComponent.java:1065)
	at javax.swing.JComponent.paintChildren(JComponent.java:889)
	at javax.swing.JComponent.paint(JComponent.java:1065)
	at javax.swing.JLayeredPane.paint(JLayeredPane.java:586)
	at javax.swing.JComponent.paintChildren(JComponent.java:889)
	at javax.swing.JComponent.paintToOffscreen(JComponent.java:5217)
	at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1579)
	at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1502)
	at javax.swing.RepaintManager.paint(RepaintManager.java:1272)
	at javax.swing.JComponent.paint(JComponent.java:1042)
	at java.awt.GraphicsCallback$PaintCallback.run(GraphicsCallback.java:39)
	at sun.awt.SunGraphicsCallback.runOneComponent(SunGraphicsCallback.java:79)
	at sun.awt.SunGraphicsCallback.runComponents(SunGraphicsCallback.java:116)
	at java.awt.Container.paint(Container.java:1978)
	at java.awt.Window.paint(Window.java:3906)
	at javax.swing.RepaintManager$4.run(RepaintManager.java:842)
	at javax.swing.RepaintManager$4.run(RepaintManager.java:814)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
	at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:814)
	at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:789)
	at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:738)
	at javax.swing.RepaintManager.access$1200(RepaintManager.java:64)
	at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1732)
	at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
	at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
	at java.awt.EventQueue.access$500(EventQueue.java:97)
	at java.awt.EventQueue$3.run(EventQueue.java:709)
	at java.awt.EventQueue$3.run(EventQueue.java:703)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

The min width at which the exception triggers depends on the amount of axis group which are displayed. The more axis group there are, the higher the min width is.

I tested version 3.6.4, 3.6.6 and the latest 3.8.2. This bug appears on all 3 versions.