A change to JComponent in the Swing workspace has revealed a bug in Container that is causing a NullPointerException when starting SwingSet2. The error message is as follows.

java.lang.NullPointerException
        at java.awt.Container.invalidate(Container.java:802)
        at javax.swing.JComponent.revalidate(JComponent.java:4297)
        at javax.swing.JComponent$1.run(JComponent.java:4303)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:167)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:437)
        at java.awt.EventDispatchThread.pumpOneEvent(EventDispatchThread.java:150)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:136)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:131)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:99)

The problem seems to be that the invalidate method is not thread-safe.