When using Netbeans 6.0, randomly from time to time, following exception is thrown from ScrollPaneLayout:

java.lang.NullPointerException
        at javax.swing.ScrollPaneLayout.preferredLayoutSize(ScrollPaneLayout.java:494)
        at java.awt.Container.preferredSize(Container.java:1669)
        at java.awt.Container.getPreferredSize(Container.java:1654)
        at javax.swing.JComponent.getPreferredSize(JComponent.java:1645)
        at java.awt.GridBagLayout.GetLayoutInfo(GridBagLayout.java:1109)
        at java.awt.GridBagLayout.GetLayoutInfo(GridBagLayout.java:910)
        at java.awt.GridBagLayout.preferredLayoutSize(GridBagLayout.java:730)
        at java.awt.Container.preferredSize(Container.java:1669)
        at java.awt.Container.getPreferredSize(Container.java:1654)
        at javax.swing.JComponent.getPreferredSize(JComponent.java:1645)
        at java.awt.BorderLayout.preferredLayoutSize(BorderLayout.java:724)
        at java.awt.Container.preferredSize(Container.java:1669)
        at java.awt.Container.getPreferredSize(Container.java:1654)
        at javax.swing.JComponent.getPreferredSize(JComponent.java:1645)
        at java.awt.GridBagLayout.GetLayoutInfo(GridBagLayout.java:1109)
        at java.awt.GridBagLayout.GetLayoutInfo(GridBagLayout.java:910)
        at java.awt.GridBagLayout.ArrangeGrid(GridBagLayout.java:2065)
        at java.awt.GridBagLayout.ArrangeGrid(GridBagLayout.java:2025)
        at java.awt.GridBagLayout.layoutContainer(GridBagLayout.java:806)
        at java.awt.Container.layout(Container.java:1485)
        at java.awt.Container.doLayout(Container.java:1474)
        at java.awt.Container.validateTree(Container.java:1572)
        at java.awt.Container.validateTree(Container.java:1579)
        at java.awt.Container.validateTree(Container.java:1579)
        at java.awt.Container.validateTree(Container.java:1579)
        at java.awt.Container.validateTree(Container.java:1579)
        at java.awt.Container.validateTree(Container.java:1579)
        at java.awt.Container.validateTree(Container.java:1579)
        at java.awt.Container.validate(Container.java:1544)
        at javax.swing.RepaintManager.validateInvalidComponents(RepaintManager.java:652)
        at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1549)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:226)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:602)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:275)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:200)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:194)
        at java.awt.Dialog$1.run(Dialog.java:1072)
        at java.awt.Dialog$3.run(Dialog.java:1126)
        at java.security.AccessController.doPrivileged(AccessController.java:0)
        at java.awt.Dialog.show(Dialog.java:1124)
        at org.netbeans.core.windows.services.NbPresenter.superShow(NbPresenter.java:834)
        at org.netbeans.core.windows.services.NbPresenter.doShow(NbPresenter.java:868)
        at org.netbeans.core.windows.services.NbPresenter.run(NbPresenter.java:856)
        at org.netbeans.core.windows.services.NbPresenter.run(NbPresenter.java:104)
        at org.openide.util.Mutex.doEventAccess(Mutex.java:1355)
        at org.openide.util.Mutex.readAccess(Mutex.java:268)
        at org.netbeans.core.windows.services.NbPresenter.show(NbPresenter.java:841)
        at java.awt.Component.show(Component.java:1455)
        at java.awt.Component.setVisible(Component.java:1407)
        at java.awt.Window.setVisible(Window.java:870)
        at java.awt.Dialog.setVisible(Dialog.java:1011)
        at org.openide.loaders.TemplateWizard.instantiateImpl(TemplateWizard.java:502)
        at org.openide.loaders.TemplateWizard.instantiate(TemplateWizard.java:369)
        at org.netbeans.modules.project.ui.actions.NewProject$2.run(NewProject.java:139)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:226)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:602)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:275)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:200)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:194)
        at java.awt.Dialog$1.run(Dialog.java:1072)
        at java.awt.Dialog$3.run(Dialog.java:1126)
        at java.security.AccessController.doPrivileged(AccessController.java:0)
        at java.awt.Dialog.show(Dialog.java:1124)
        at org.netbeans.core.windows.services.NbPresenter.superShow(NbPresenter.java:834)
        at org.netbeans.core.windows.services.NbPresenter.doShow(NbPresenter.java:868)
        at org.netbeans.core.windows.services.NbPresenter.run(NbPresenter.java:856)
        at org.netbeans.core.windows.services.NbPresenter.run(NbPresenter.java:104)
        at org.openide.util.Mutex.doEventAccess(Mutex.java:1355)
        at org.openide.util.Mutex.readAccess(Mutex.java:268)
        at org.netbeans.core.windows.services.NbPresenter.show(NbPresenter.java:841)
        at java.awt.Component.show(Component.java:1455)
        at java.awt.Component.setVisible(Component.java:1407)
        at java.awt.Window.setVisible(Window.java:870)
        at java.awt.Dialog.setVisible(Dialog.java:1011)
        at org.openide.loaders.TemplateWizard.instantiateImpl(TemplateWizard.java:502)
        at org.openide.loaders.TemplateWizard.instantiate(TemplateWizard.java:369)
        at org.netbeans.modules.project.ui.actions.NewProject$2.run(NewProject.java:139)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:226)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:602)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:275)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:200)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:194)
        at java.awt.Dialog$1.run(Dialog.java:1072)
        at java.awt.Dialog$3.run(Dialog.java:1126)
        at java.security.AccessController.doPrivileged(AccessController.java:0)
        at java.awt.Dialog.show(Dialog.java:1124)
        at org.netbeans.core.windows.services.NbPresenter.superShow(NbPresenter.java:834)
        at org.netbeans.core.windows.services.NbPresenter.doShow(NbPresenter.java:868)
        at org.netbeans.core.windows.services.NbPresenter.run(NbPresenter.java:856)
        at org.netbeans.core.windows.services.NbPresenter.run(NbPresenter.java:104)
        at org.openide.util.Mutex.doEventAccess(Mutex.java:1355)
        at org.openide.util.Mutex.readAccess(Mutex.java:268)
        at org.netbeans.core.windows.services.NbPresenter.show(NbPresenter.java:841)
        at java.awt.Component.show(Component.java:1455)
        at java.awt.Component.setVisible(Component.java:1407)
        at java.awt.Window.setVisible(Window.java:870)
        at java.awt.Dialog.setVisible(Dialog.java:1011)
        at org.openide.loaders.TemplateWizard.instantiateImpl(TemplateWizard.java:502)
        at org.openide.loaders.TemplateWizard.instantiate(TemplateWizard.java:369)
        at org.netbeans.modules.project.ui.actions.NewProject$2.run(NewProject.java:139)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:226)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:602)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:275)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:200)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:194)
        at java.awt.Dialog$1.run(Dialog.java:1072)
        at java.awt.Dialog$3.run(Dialog.java:1126)
        at java.security.AccessController.doPrivileged(AccessController.java:0)
        at java.awt.Dialog.show(Dialog.java:1124)
        at org.netbeans.core.windows.services.NbPresenter.superShow(NbPresenter.java:834)
        at org.netbeans.core.windows.services.NbPresenter.doShow(NbPresenter.java:868)
        at org.netbeans.core.windows.services.NbPresenter.run(NbPresenter.java:856)
        at org.netbeans.core.windows.services.NbPresenter.run(NbPresenter.java:104)
        at org.openide.util.Mutex.doEventAccess(Mutex.java:1355)
        at org.openide.util.Mutex.readAccess(Mutex.java:268)
        at org.netbeans.core.windows.services.NbPresenter.show(NbPresenter.java:841)
        at java.awt.Component.show(Component.java:1455)
        at java.awt.Component.setVisible(Component.java:1407)
        at java.awt.Window.setVisible(Window.java:870)
        at java.awt.Dialog.setVisible(Dialog.java:1011)
        at org.openide.loaders.TemplateWizard.instantiateImpl(TemplateWizard.java:502)
        at org.openide.loaders.TemplateWizard.instantiate(TemplateWizard.java:369)
        at org.netbeans.modules.project.ui.actions.NewProject$2.run(NewProject.java:139)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:226)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:602)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:275)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:200)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:190)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:185)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:177)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:138)

It seems to be regression in newer JDK builds, namely "Java HotSpot(TM) Client VM, 12.0-b01" version. To see details in Netbeans exception reporter, please go to http://statistics.netbeans.org/analytics/detail.do?id=17307

Original netbeans issue entered in Issuezilla is here:
http://www.netbeans.org/issues/show_bug.cgi?id=126466