This occurs on both NT4 and Solaris7 with kestrel-M.

To reproduce:
-start up the SwingSet demo (version 1.1)
-select the InternalFrame tab
-click the Make button on the Frame Creator window
-iconify the newly created internal frame
-select a new look and feel from the Options menu

The folling NullPointerException is thrown:

Exception occurred during event dispatching:
java.lang.NullPointerException
        at javax.swing.plaf.basic.BasicInternalFrameUI$ComponentHandler.componentResized(BasicInternalFrameUI.java:998)
        at java.awt.Component.processComponentEvent(Component.java:3490)
        at java.awt.Component.processEvent(Component.java:3448)
        at java.awt.Container.processEvent(Container.java:1253)
        at java.awt.Component.dispatchEventImpl(Component.java:2524)
        at java.awt.Container.dispatchEventImpl(Container.java:1302)
        at java.awt.Component.dispatchEvent(Component.java:2438)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:302)
        at java.awt.EventDispatchThread.pumpOneEvent(EventDispatchThread.java:105)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:95)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:86)