This in Q-build 200408011800
(the version selector above is really confusing - what do we 
choose to submit bugs in 4.0 builds of netbeans - the FFJ 
versions ?)
I Imagine this may be OSX specific, but not sure.
When trying to add another project classpath to a project 
(Project->properties->compiling sources->add project) the file 
browsing dialogue throws the following exception when you try 
to open or select of folder :

java.lang.NullPointerException
	at 
org.openide.filesystems.FileUtil.normalizeFile(FileUtil.java:959)
	at 
org.netbeans.modules.java.j2seproject.ui.customizer.AntArtifact
Chooser.propertyChange(AntArtifactChooser.java:120)
	at 
javax.swing.event.SwingPropertyChangeSupport.firePropertyCha
nge(SwingPropertyChangeSupport.java:264)
	at 
javax.swing.event.SwingPropertyChangeSupport.firePropertyCha
nge(SwingPropertyChangeSupport.java:232)
	at 
javax.swing.JComponent.firePropertyChange(JComponent.java:
3819)
	at 
javax.swing.JFileChooser.setSelectedFile(JFileChooser.java:454)
	at 
apple.laf.AquaFileChooserUI$SelectionListener.valueChanged(Aq
uaFileChooserUI.java:601)
	at 
javax.swing.DefaultListSelectionModel.fireValueChanged(Default
ListSelectionModel.java:187)
	at 
javax.swing.DefaultListSelectionModel.fireValueChanged(Default
ListSelectionModel.java:167)
	at 
javax.swing.DefaultListSelectionModel.fireValueChanged(Default
ListSelectionModel.java:214)
	at 
javax.swing.DefaultListSelectionModel.changeSelection(DefaultLi
stSelectionModel.java:402)
	at 
javax.swing.DefaultListSelectionModel.changeSelection(DefaultLi
stSelectionModel.java:411)
	at 
javax.swing.DefaultListSelectionModel.removeSelectionInterval(D
efaultListSelectionModel.java:481)
	at 
javax.swing.DefaultListSelectionModel.clearSelection(DefaultListS
electionModel.java:416)
	at javax.swing.JTable.clearSelection(JTable.java:1262)
	at 
apple.laf.AquaFileChooserUI.openDirectory(AquaFileChooserUI.ja
va:636)
	at 
apple.laf.AquaFileChooserUI$DoubleClickListener.mouseClicked(
AquaFileChooserUI.java:658)
	at 
java.awt.AWTEventMulticaster.mouseClicked(AWTEventMulticaste
r.java:212)
	at 
java.awt.Component.processMouseEvent(Component.java:5103)
	at java.awt.Component.processEvent(Component.java:
4897)
	at java.awt.Container.processEvent(Container.java:1569)
	at java.awt.Component.dispatchEventImpl(Component.java:
3615)
	at java.awt.Container.dispatchEventImpl(Container.java:
1627)
	at java.awt.Component.dispatchEvent(Component.java:
3477)
	at 
java.awt.LightweightDispatcher.retargetMouseEvent(Container.ja
va:3483)
	at 
java.awt.LightweightDispatcher.processMouseEvent(Container.ja
va:3207)
	at 
java.awt.LightweightDispatcher.dispatchEvent(Container.java:
3128)
	at java.awt.Container.dispatchEventImpl(Container.java:
1613)
	at java.awt.Window.dispatchEventImpl(Window.java:1606)
	at java.awt.Component.dispatchEvent(Component.java:
3477)
[catch] at java.awt.EventQueue.dispatchEvent(EventQueue.java:
456)
	at 
java.awt.EventDispatchThread.pumpOneEventForHierarchy(Event
DispatchThread.java:234)
	at 
java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDis
patchThread.java:184)
	at 
java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDis
patchThread.java:174)
	at java.awt.Dialog$1.run(Dialog.java:540)
	at java.awt.Dialog.show(Dialog.java:561)
	at javax.swing.JFileChooser.showDialog(JFileChooser.java:
696)
	at 
javax.swing.JFileChooser.showOpenDialog(JFileChooser.java:599)
	at 
org.netbeans.modules.java.j2seproject.ui.customizer.AntArtifact
Chooser.showDialog(AntArtifactChooser.java:188)
	at 
org.netbeans.modules.java.j2seproject.ui.customizer.VisualClass
pathSupport$ClasspathSupportListener.actionPerformed(VisualCl
asspathSupport.java:332)
	at 
javax.swing.AbstractButton.fireActionPerformed(AbstractButton.j
ava:1819)
	at 
javax.swing.AbstractButton$ForwardActionEvents.actionPerform
ed(AbstractButton.java:1872)
	at 
javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButt
onModel.java:420)
	at 
javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.
java:258)
	at 
javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicB
uttonListener.java:247)
	at 
java.awt.Component.processMouseEvent(Component.java:5100)
	at java.awt.Component.processEvent(Component.java:
4897)
	at java.awt.Container.processEvent(Container.java:1569)
	at java.awt.Component.dispatchEventImpl(Component.java:
3615)
	at java.awt.Container.dispatchEventImpl(Container.java:
1627)
	at java.awt.Component.dispatchEvent(Component.java:
3477)
	at 
java.awt.LightweightDispatcher.retargetMouseEvent(Container.ja
va:3483)
	at 
java.awt.LightweightDispatcher.processMouseEvent(Container.ja
va:3198)
	at 
java.awt.LightweightDispatcher.dispatchEvent(Container.java:
3128)
	at java.awt.Container.dispatchEventImpl(Container.java:
1613)
	at java.awt.Window.dispatchEventImpl(Window.java:1606)
	at java.awt.Component.dispatchEvent(Component.java:
3477)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:
456)
	at 
java.awt.EventDispatchThread.pumpOneEventForHierarchy(Event
DispatchThread.java:234)
	at 
java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDis
patchThread.java:184)
	at 
java.awt.EventDispatchThread.pumpEvents(EventDispatchThread
.java:178)
	at 
java.awt.EventDispatchThread.pumpEvents(EventDispatchThread
.java:170)
	at 
java.awt.EventDispatchThread.run(EventDispatchThread.java:
100)