This bug was originally marked as duplicate of bug 140423, that is already resolved. This bug is still valid, so this seems to be another bug, but it might be related.

Build: NetBeans IDE 6.9.1 (Build 201011082200)
VM: Java HotSpot(TM) Client VM, 19.0-b09, Java(TM) SE Runtime Environment, 1.6.0_23-b05
OS: Windows XP

User Comments:
GUEST: Deleted a folder, didn't disappear from the Projects list, then tried to expand/collapse the parent folder.

twoelectric: Opened a new Kenai project. This may be due to the warning of "source folder" not defined.

GUEST: Updating files via CVS; an expanded portion of the tree became blank.  The space that should have been taken up by the file display was simply white.  I closed & re-expanded portions of the tree with similar results.  After doing so several times, the error seems to have resolved

GUEST: deleted the build folder

GUEST: Updating from CVS.  Everything below web pages in my web app became unclickable

rupertkey: [NB6.5Beta1] C/C++ Project: In the Classes panel, expanding the C src file name to show functions gives exception (although the tree shows correct list of functions).

GUEST: Sorry,

My english is not good!!

When I open package the Netbeans show me this message.

I am not use Swing, my project is JSF2 whith spring.

Bruno Hahn Barreto

GUEST: Estava tentando excluir uma pasta

jrcampins: deleteing a folder




Stacktrace: 
java.lang.NullPointerException
   at com.sun.java.swing.plaf.windows.WindowsTreeUI.ensureRowsAreVisible(WindowsTreeUI.java:74)
   at javax.swing.plaf.basic.BasicTreeUI.toggleExpandState(BasicTreeUI.java:2208)
   at javax.swing.plaf.basic.BasicTreeUI.handleExpandControlClick(BasicTreeUI.java:2191)
   at javax.swing.plaf.basic.BasicTreeUI.checkForClickInExpandControl(BasicTreeUI.java:2149)
   at javax.swing.plaf.basic.BasicTreeUI$Handler.handleSelection(BasicTreeUI.java:3511)
   at javax.swing.plaf.basic.BasicTreeUI$Handler.mousePressedDND(BasicTreeUI.java:3497)