FULL PRODUCT VERSION :
java version "1.6.0-rc"
Java(TM) SE Runtime Environment (build 1.6.0-rc-b98)
Java HotSpot(TM) Client VM (build 1.6.0-rc-b98, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 5.2.3790]

A DESCRIPTION OF THE PROBLEM :
This bug report is for a regression for closed bug: 4264002 .

This bug has been encountered in JRE 1.6.
see 4264002 for details.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
When a JTree's updateUI() is called as a result of a key event, a NullPointerExcpetion is thrown from the JTree$Handler's isNavigationKey() method.

See the example code in 4264002 for an example of the problem.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The library keyAdapter() methods should check for null elements, so as not to throw a NullPointerException
ACTUAL -
A NullPointerException is thrown

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javax.swing.plaf.basic.BasicTreeUI$Handler.isNavigationKey(Unknown Source)
at javax.swing.plaf.basic.BasicTreeUI$Handler.keyPressed(Unknown Source)
at java.awt.AWTEventMulticaster.keyPressed(Unknown Source)
at java.awt.Component.processKeyEvent(Unknown Source)
at javax.swing.JComponent.processKeyEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.KeyboardFocusManager.redispatchEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.dispatchEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
See the example code in 4264002 for an example of the problem.
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
  Bug 4264002 states that running updateUI() wrapped in a SwingUtilities.invokeLater() is a potential workaround.

This is not a practical workaround in all cases (although when possible, it does fix this particular problem).