Eclipse NullPointerException reported when launching debug

[paulvi]

java.lang.NullPointerException
    at org.eclipse.ui.internal.navigator.resources.nested.NestedProjectManager.isShownAsNested(NestedProjectManager.java:106)
    at org.eclipse.ui.internal.navigator.resources.nested.HideTopLevelProjectIfNested.select(HideTopLevelProjectIfNested.java:50)
    at org.eclipse.jface.viewers.ViewerFilter.filter(ViewerFilter.java:56)
    at org.eclipse.jface.viewers.StructuredViewer.getFilteredChildren(StructuredViewer.java:910)
    at org.eclipse.jface.viewers.AbstractTreeViewer.getSortedChildren(AbstractTreeViewer.java:617)
    at org.eclipse.jface.viewers.AbstractTreeViewer.updateChildren(AbstractTreeViewer.java:2647)
    at org.eclipse.jface.viewers.AbstractTreeViewer.internalRefreshStruct(AbstractTreeViewer.java:1916)
    at org.eclipse.jface.viewers.TreeViewer.internalRefreshStruct(TreeViewer.java:684)
    at org.eclipse.jface.viewers.AbstractTreeViewer.internalRefresh(AbstractTreeViewer.java:1891)
    at org.eclipse.jface.viewers.AbstractTreeViewer.internalRefresh(AbstractTreeViewer.java:1841)
    at org.eclipse.ui.navigator.CommonViewer.internalRefresh(CommonViewer.java:527)
    at org.eclipse.jface.viewers.StructuredViewer$8.run(StructuredViewer.java:1554)
    at org.eclipse.jface.viewers.StructuredViewer.preservingSelection(StructuredViewer.java:1462)
    at org.eclipse.jface.viewers.TreeViewer.preservingSelection(TreeViewer.java:366)
    at org.eclipse.jface.viewers.StructuredViewer.preservingSelection(StructuredViewer.java:1423)
    at org.eclipse.jface.viewers.StructuredViewer.refresh(StructuredViewer.java:1551)
    at org.eclipse.jface.viewers.ColumnViewer.refresh(ColumnViewer.java:534)
    at org.eclipse.ui.navigator.CommonViewer.refresh(CommonViewer.java:344)
    at org.eclipse.wst.jsdt.internal.ui.packageview.PackageExplorerContentProvider$7.run(PackageExplorerContentProvider.java:1512)
    at org.eclipse.wst.jsdt.internal.ui.packageview.PackageExplorerContentProvider.runUpdates(PackageExplorerContentProvider.java:198)
    at org.eclipse.wst.jsdt.internal.ui.packageview.PackageExplorerContentProvider.runPendingUpdates(PackageExplorerContentProvider.java:190)
    at org.eclipse.wst.jsdt.internal.ui.packageview.PackageExplorerContentProvider$1.runInUIThread(PackageExplorerContentProvider.java:168)
    at org.eclipse.ui.progress.UIJob$1.run(UIJob.java:97)
    at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:35)
    at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:135)
    at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:4155)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3772)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$4.run(PartRenderingEngine.java:1127)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:337)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1018)
    at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:156)
    at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:654)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:337)
    at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:598)
    at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:150)
    at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:139)
    at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:380)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:235)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:669)
    at org.eclipse.equinox.launcher.Main.basicRun(Main.java:608)
    at org.eclipse.equinox.launcher.Main.run(Main.java:1515)