This bug was originally marked as duplicate of bug 191781, that is already resolved. This bug is still valid, so this seems to be another bug, but it might be related.

Build: NetBeans IDE Dev (Build 201012060001)
VM: Java HotSpot(TM) Client VM, 17.1-b03, Java(TM) SE Runtime Environment, 1.6.0_22-b04
OS: Windows XP

User Comments:
GUEST: Debugging an application

bartvdc: expand project. libraries folder view  is empty

stefan79: Expand in Project-View.

GUEST: I tried to add a netbeans plattform wrapper modul to a netbeans plattform application

bestmike007: I don't know, it just happened..

GUEST: Don't remember

GUEST: going through files in navigatino pane

esmithbss: Expanding the Tree view of my Project.  There are 4 projects and when expanding the top item, the system leaves a large blank area below the package tree.

GUEST: I add some new dependecies to teh pom.xml and the project window's view became crazy.

earlGrey: Only switched tab from "Projects" to "Services".




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)