OK .. Continuing to appreciate the assistance:
!ENTRY org.eclipse.ui.workbench 4 2 2015-04-30 11:49:12.420
!MESSAGE Problems occurred when invoking code from plug-in: "org.eclipse.ui.workbench".
!STACK 0
java.lang.NullPointerException
at org.eclipse.ui.internal.NavigationHistory$1.updateNavigationHistory(NavigationHistory.java:123)
at org.eclipse.ui.internal.NavigationHistory$1.partClosed(NavigationHistory.java:100)
at org.eclipse.ui.internal.WorkbenchPage$23.run(WorkbenchPage.java:4966)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.ui.internal.WorkbenchPage.firePartClosed(WorkbenchPage.java:4963)
at org.eclipse.ui.internal.e4.compatibility.CompatibilityPart$1.handleEvent(CompatibilityPart.java:98)
at org.eclipse.e4.ui.services.internal.events.UIEventHandler$1.run(UIEventHandler.java:40)
at org.eclipse.swt.widgets.Synchronizer.syncExec(Synchronizer.java:187)
at org.eclipse.ui.internal.UISynchronizer.syncExec(UISynchronizer.java:156)
at org.eclipse.swt.widgets.Display.syncExec(Display.java:4732)
at org.eclipse.e4.ui.internal.workbench.swt.E4Application$1.syncExec(E4Application.java:218)
at org.eclipse.e4.ui.services.internal.events.UIEventHandler.handleEvent(UIEventHandler.java:36)
at org.eclipse.equinox.internal.event.EventHandlerWrapper.handleEvent(EventHandlerWrapper.java:197)
at org.eclipse.equinox.internal.event.EventHandlerTracker.dispatchEvent(EventHandlerTracker.java:197)
at org.eclipse.equinox.internal.event.EventHandlerTracker.dispatchEvent(EventHandlerTracker.java:1)
at org.eclipse.osgi.framework.eventmgr.EventManager.dispatchEvent(EventManager.java:230)
at org.eclipse.osgi.framework.eventmgr.ListenerQueue.dispatchEventSynchronous(ListenerQueue.java:148)
at org.eclipse.equinox.internal.event.EventAdminImpl.dispatchEvent(EventAdminImpl.java:135)
at org.eclipse.equinox.internal.event.EventAdminImpl.sendEvent(EventAdminImpl.java:78)
at org.eclipse.equinox.internal.event.EventComponent.sendEvent(EventComponent.java:39)
at org.eclipse.e4.ui.services.internal.events.EventBroker.send(EventBroker.java:81)
at org.eclipse.e4.ui.internal.workbench.UIEventPublisher.notifyChanged(UIEventPublisher.java:59)
at org.eclipse.emf.common.notify.impl.BasicNotifierImpl.eNotify(BasicNotifierImpl.java:374)
at org.eclipse.e4.ui.model.application.ui.impl.UIElementImpl.setWidget(UIElementImpl.java:261)
at org.eclipse.e4.ui.workbench.renderers.swt.SWTPartRenderer.unbindWidget(SWTPartRenderer.java:150)
at org.eclipse.e4.ui.workbench.renderers.swt.SWTPartRenderer.disposeWidget(SWTPartRenderer.java:173)
at org.eclipse.e4.ui.workbench.renderers.swt.ContributedPartRenderer.disposeWidget(ContributedPartRenderer.java:266)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeRemoveGui(PartRenderingEngine.java:933)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.access$3(PartRenderingEngine.java:862)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$8.run(PartRenderingEngine.java:857)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.removeGui(PartRenderingEngine.java:841)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$1.handleEvent(PartRenderingEngine.java:160)
at org.eclipse.e4.ui.services.internal.events.UIEventHandler$1.run(UIEventHandler.java:40)
at org.eclipse.swt.widgets.Synchronizer.syncExec(Synchronizer.java:187)
at org.eclipse.ui.internal.UISynchronizer.syncExec(UISynchronizer.java:156)
at org.eclipse.swt.widgets.Display.syncExec(Display.java:4732)
at org.eclipse.e4.ui.internal.workbench.swt.E4Application$1.syncExec(E4Application.java:218)
at org.eclipse.e4.ui.services.internal.events.UIEventHandler.handleEvent(UIEventHandler.java:36)
at org.eclipse.equinox.internal.event.EventHandlerWrapper.handleEvent(EventHandlerWrapper.java:197)
at org.eclipse.equinox.internal.event.EventHandlerTracker.dispatchEvent(EventHandlerTracker.java:197)
at org.eclipse.equinox.internal.event.EventHandlerTracker.dispatchEvent(EventHandlerTracker.java:1)
at org.eclipse.osgi.framework.eventmgr.EventManager.dispatchEvent(EventManager.java:230)
at org.eclipse.osgi.framework.eventmgr.ListenerQueue.dispatchEventSynchronous(ListenerQueue.java:148)
at org.eclipse.equinox.internal.event.EventAdminImpl.dispatchEvent(EventAdminImpl.java:135)
at org.eclipse.equinox.internal.event.EventAdminImpl.sendEvent(EventAdminImpl.java:78)
at org.eclipse.equinox.internal.event.EventComponent.sendEvent(EventComponent.java:39)
at org.eclipse.e4.ui.services.internal.events.EventBroker.send(EventBroker.java:81)
at org.eclipse.e4.ui.internal.workbench.UIEventPublisher.notifyChanged(UIEventPublisher.java:59)
at org.eclipse.emf.common.notify.impl.BasicNotifierImpl.eNotify(BasicNotifierImpl.java:374)
at org.eclipse.e4.ui.model.application.ui.impl.UIElementImpl.setToBeRendered(UIElementImpl.java:303)
at org.eclipse.e4.ui.internal.workbench.PartServiceImpl.hidePart(PartServiceImpl.java:1281)
at org.eclipse.e4.ui.internal.workbench.PartServiceImpl.hidePart(PartServiceImpl.java:1215)
at org.eclipse.e4.ui.workbench.renderers.swt.StackRenderer.closePart(StackRenderer.java:1218)
at org.eclipse.e4.ui.workbench.renderers.swt.StackRenderer.access$3(StackRenderer.java:1200)
at org.eclipse.e4.ui.workbench.renderers.swt.StackRenderer$12.close(StackRenderer.java:1092)
at org.eclipse.swt.custom.CTabFolder.onMouse(CTabFolder.java:1874)
at org.eclipse.swt.custom.CTabFolder$1.handleEvent(CTabFolder.java:288)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4199)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1467)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1490)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1475)
at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:1279)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4042)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3669)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:1151)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1032)
at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:148)
at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:636)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:579)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:150)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:135)
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:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:648)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:603)
at org.eclipse.equinox.launcher.Main.run(Main.java:1465)