java.lang.RuntimeException: org.eclipse.core.runtime.CoreException: org.eclipse.core.runtime.AssertionFailedException: null argument:

org.eclipse.core.runtime.AssertionFailedException: null argument:	at org.eclipse.core.runtime.Assert.isNotNull(Assert.java:86)	at org.eclipse.core.runtime.Assert.isNotNull(Assert.java:74)	at org.python.pydev.plugin.nature.PythonNatureStore.getRootNodeInXml(PythonNatureStore.java:291)	at org.python.pydev.plugin.nature.PythonNatureStore.findPropertyNodeInXml(PythonNatureStore.java:329)	at org.python.pydev.plugin.nature.PythonNatureStore.getPathPropertyFromXml(PythonNatureStore.java:596)	at org.python.pydev.plugin.nature.PythonNatureStore.getPathProperty(PythonNatureStore.java:176)	at org.python.pydev.plugin.nature.PythonPathNature.getProjectSourcePath(PythonPathNature.java:247)	at org.python.pydev.plugin.nature.PythonPathNature.getProjectSourcePathSet(PythonPathNature.java:234)	at org.python.pydev.navigator.PythonModelProvider.doWrapPossibleSourceFolder(PythonModelProvider.java:467)	at org.python.pydev.navigator.PythonModelProvider.doWrap(PythonModelProvider.java:415)	at org.python.pydev.navigator.PythonModelProvider.wrapChildren(PythonModelProvider.java:372)	at org.python.pydev.navigator.PythonModelProvider.convertToPythonElementsAddOrRemove(PythonModelProvider.java:273)	at org.python.pydev.navigator.PythonModelProvider.getPipelinedChildren(PythonModelProvider.java:72)	at org.python.pydev.navigator.PythonModelProvider.getPipelinedElements(PythonModelProvider.java:86)	at org.eclipse.ui.internal.navigator.NavigatorContentServiceContentProvider.pipelineElements(NavigatorContentServiceContentProvider.java:363)	at org.eclipse.ui.internal.navigator.NavigatorContentServiceContentProvider.getElements(NavigatorContentServiceContentProvider.java:170)	at org.eclipse.jface.viewers.StructuredViewer.getRawChildren(StructuredViewer.java:937)	at org.eclipse.jface.viewers.ColumnViewer.getRawChildren(ColumnViewer.java:703)	at org.eclipse.jface.viewers.AbstractTreeViewer.getRawChildren(AbstractTreeViewer.java:1330)	at org.eclipse.jface.viewers.TreeViewer.getRawChildren(TreeViewer.java:385)	at org.eclipse.jface.viewers.AbstractTreeViewer.getFilteredChildren(AbstractTreeViewer.java:636)	at org.eclipse.jface.viewers.AbstractTreeViewer.getSortedChildren(AbstractTreeViewer.java:602)	at org.eclipse.jface.viewers.AbstractTreeViewer$1.run(AbstractTreeViewer.java:799)	at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)	at org.eclipse.jface.viewers.AbstractTreeViewer.createChildren(AbstractTreeViewer.java:776)	at org.eclipse.jface.viewers.TreeViewer.createChildren(TreeViewer.java:634)	at org.eclipse.jface.viewers.AbstractTreeViewer.internalInitializeTree(AbstractTreeViewer.java:1490)	at org.eclipse.jface.viewers.TreeViewer.internalInitializeTree(TreeViewer.java:823)	at org.eclipse.jface.viewers.AbstractTreeViewer$5.run(AbstractTreeViewer.java:1474)	at org.eclipse.jface.viewers.StructuredViewer.preservingSelection(StructuredViewer.java:1365)	at org.eclipse.jface.viewers.TreeViewer.preservingSelection(TreeViewer.java:397)	at org.eclipse.jface.viewers.StructuredViewer.preservingSelection(StructuredViewer.java:1328)	at org.eclipse.jface.viewers.AbstractTreeViewer.inputChanged(AbstractTreeViewer.java:1467)	at org.eclipse.jface.viewers.ContentViewer.setInput(ContentViewer.java:251)	at org.eclipse.jface.viewers.StructuredViewer.setInput(StructuredViewer.java:1603)	at org.eclipse.ui.navigator.CommonNavigator.createPartControl(CommonNavigator.java:176)	at org.python.pydev.navigator.ui.PydevPackageExplorer.createPartControl(PydevPackageExplorer.java:115)	at org.eclipse.ui.internal.ViewReference.createPartHelper(ViewReference.java:371)	at org.eclipse.ui.internal.ViewReference.createPart(ViewReference.java:230)	at org.eclipse.ui.internal.WorkbenchPartReference.getPart(WorkbenchPartReference.java:594)	at org.eclipse.ui.internal.PartPane.setVisible(PartPane.java:306)	at org.eclipse.ui.internal.ViewPane.setVisible(ViewPane.java:531)	at org.eclipse.ui.internal.presentations.PresentablePart.setVisible(PresentablePart.java:180)	at org.eclipse.ui.internal.presentations.util.PresentablePartFolder.select(PresentablePartFolder.java:270)	at org.eclipse.ui.internal.presentations.util.LeftToRightTabOrder.select(LeftToRightTabOrder.java:65)	at org.eclipse.ui.internal.presentations.util.TabbedStackPresentation.selectPart(TabbedStackPresentation.java:473)	at org.eclipse.ui.internal.PartStack.refreshPresentationSelection(PartStack.java:1256)	at org.eclipse.ui.internal.PartStack.createControl(PartStack.java:668)	at org.eclipse.ui.internal.PartStack.createControl(PartStack.java:576)	at org.eclipse.ui.internal.PartSashContainer.createControl(PartSashContainer.java:568)	at org.eclipse.ui.internal.PerspectiveHelper.activate(PerspectiveHelper.java:271)	at org.eclipse.ui.internal.Perspective.onActivate(Perspective.java:964)	at org.eclipse.ui.internal.WorkbenchPage.onActivate(WorkbenchPage.java:2593)	at org.eclipse.ui.internal.WorkbenchWindow$25.run(WorkbenchWindow.java:2869)	at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)	at org.eclipse.ui.internal.WorkbenchWindow.setActivePage(WorkbenchWindow.java:2850)	at org.eclipse.ui.internal.WorkbenchWindow$19.runWithException(WorkbenchWindow.java:2167)	at org.eclipse.ui.internal.StartupThreading$StartupRunnable.run(StartupThreading.java:31)	at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:35)	at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:133)	at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:3800)	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3425)	at org.eclipse.ui.application.WorkbenchAdvisor.openWindows(WorkbenchAdvisor.java:803)	at org.eclipse.ui.internal.Workbench$27.runWithException(Workbench.java:1361)	at org.eclipse.ui.internal.StartupThreading$StartupRunnable.run(StartupThreading.java:31)	at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:35)	at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:133)	at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:3800)	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3425)	at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2293)	at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2198)	at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:493)	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:288)	at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:488)	at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)	at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:113)	at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:193)	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:382)	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179)	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)	at java.lang.reflect.Method.invoke(Unknown Source)	at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:549)	at org.eclipse.equinox.launcher.Main.basicRun(Main.java:504)	at org.eclipse.equinox.launcher.Main.run(Main.java:1236)