Not sure how I got the error, but I just restarted a workspace after deleting some projects in previous session.

At startup I got this error:

java.lang.NullPointerException
at org.jboss.tools.ws.jaxrs.ui.cnf.UriMappingsContentProvider.dispose(UriMappingsContentProvider.java:116)
at org.eclipse.ui.internal.navigator.extensions.SafeDelegateTreeContentProvider$1.run(SafeDelegateTreeContentProvider.java:76)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.ui.internal.navigator.extensions.SafeDelegateTreeContentProvider.dispose(SafeDelegateTreeContentProvider.java:74)
at org.eclipse.ui.internal.navigator.extensions.NavigatorContentExtension$3.run(NavigatorContentExtension.java:210)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.ui.internal.navigator.extensions.NavigatorContentExtension.dispose(NavigatorContentExtension.java:207)
at org.eclipse.ui.internal.navigator.NavigatorContentService.dispose(NavigatorContentService.java:355)
at org.eclipse.ui.navigator.CommonViewer.dispose(CommonViewer.java:251)
at org.eclipse.ui.navigator.CommonViewer.handleDispose(CommonViewer.java:239)
at org.eclipse.jface.viewers.ContentViewer$2.widgetDisposed(ContentViewer.java:214)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:123)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4166)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1466)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1489)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1470)
at org.eclipse.swt.widgets.Widget.release(Widget.java:1308)
at org.eclipse.swt.widgets.Control.release(Control.java:2861)
at org.eclipse.swt.widgets.Composite.releaseChildren(Composite.java:910)
at org.eclipse.swt.widgets.Widget.release(Widget.java:1311)
at org.eclipse.swt.widgets.Control.release(Control.java:2861)
at org.eclipse.swt.widgets.Composite.releaseChildren(Composite.java:910)
at org.eclipse.swt.widgets.Widget.release(Widget.java:1311)
at org.eclipse.swt.widgets.Control.release(Control.java:2861)
at org.eclipse.swt.widgets.Widget.dispose(Widget.java:671)
at org.eclipse.e4.ui.workbench.renderers.swt.SWTPartRenderer.disposeWidget(SWTPartRenderer.java:152)
at org.eclipse.e4.ui.workbench.renderers.swt.ContributedPartRenderer.disposeWidget(ContributedPartRenderer.java:273)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeRemoveGui(PartRenderingEngine.java:899)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.access$3(PartRenderingEngine.java:828)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$8.run(PartRenderingEngine.java:823)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.removeGui(PartRenderingEngine.java:808)
at org.eclipse.e4.ui.workbench.renderers.swt.ElementReferenceRenderer.disposeWidget(ElementReferenceRenderer.java:109)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeRemoveGui(PartRenderingEngine.java:899)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.access$3(PartRenderingEngine.java:828)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$8.run(PartRenderingEngine.java:823)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.removeGui(PartRenderingEngine.java:808)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeRemoveGui(PartRenderingEngine.java:853)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.access$3(PartRenderingEngine.java:828)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$8.run(PartRenderingEngine.java:823)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.removeGui(PartRenderingEngine.java:808)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeRemoveGui(PartRenderingEngine.java:853)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.access$3(PartRenderingEngine.java:828)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$8.run(PartRenderingEngine.java:823)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.removeGui(PartRenderingEngine.java:808)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeRemoveGui(PartRenderingEngine.java:860)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.access$3(PartRenderingEngine.java:828)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$8.run(PartRenderingEngine.java:823)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.removeGui(PartRenderingEngine.java:808)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeRemoveGui(PartRenderingEngine.java:853)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.access$3(PartRenderingEngine.java:828)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$8.run(PartRenderingEngine.java:823)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.removeGui(PartRenderingEngine.java:808)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeRemoveGui(PartRenderingEngine.java:860)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.access$3(PartRenderingEngine.java:828)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$8.run(PartRenderingEngine.java:823)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.removeGui(PartRenderingEngine.java:808)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeRemoveGui(PartRenderingEngine.java:860)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.access$3(PartRenderingEngine.java:828)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$8.run(PartRenderingEngine.java:823)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.removeGui(PartRenderingEngine.java:808)
at org.eclipse.ui.internal.WorkbenchWindow.hardClose(WorkbenchWindow.java:1598)
at org.eclipse.ui.internal.WorkbenchWindow.busyClose(WorkbenchWindow.java:1231)
at org.eclipse.ui.internal.WorkbenchWindow.access$14(WorkbenchWindow.java:1198)
at org.eclipse.ui.internal.WorkbenchWindow$10.run(WorkbenchWindow.java:1261)
at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
at org.eclipse.ui.internal.WorkbenchWindow.close(WorkbenchWindow.java:1259)
at org.eclipse.ui.internal.Workbench$14.run(Workbench.java:1096)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.ui.internal.Workbench.busyClose(Workbench.java:1079)
at org.eclipse.ui.internal.Workbench.access$19(Workbench.java:1024)
at org.eclipse.ui.internal.Workbench$19.run(Workbench.java:1327)
at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
at org.eclipse.ui.internal.Workbench.close(Workbench.java:1325)
at org.eclipse.ui.internal.Workbench.restart(Workbench.java:2480)
at org.eclipse.ui.internal.handlers.RestartWorkbenchHandler.execute(RestartWorkbenchHandler.java:31)
at org.eclipse.ui.internal.handlers.HandlerProxy.execute(HandlerProxy.java:290)
at org.eclipse.ui.internal.handlers.E4HandlerProxy.execute(E4HandlerProxy.java:90)
at sun.reflect.GeneratedMethodAccessor86.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:56)
at org.eclipse.e4.core.internal.di.InjectorImpl.invokeUsingClass(InjectorImpl.java:243)
at org.eclipse.e4.core.internal.di.InjectorImpl.invoke(InjectorImpl.java:224)
at org.eclipse.e4.core.contexts.ContextInjectionFactory.invoke(ContextInjectionFactory.java:132)
at org.eclipse.e4.core.commands.internal.HandlerServiceHandler.execute(HandlerServiceHandler.java:167)
at org.eclipse.core.commands.Command.executeWithChecks(Command.java:499)
at org.eclipse.core.commands.ParameterizedCommand.executeWithChecks(ParameterizedCommand.java:508)
at org.eclipse.e4.core.commands.internal.HandlerServiceImpl.executeHandler(HandlerServiceImpl.java:213)
at org.eclipse.e4.ui.workbench.renderers.swt.HandledContributionItem.executeItem(HandledContributionItem.java:850)
at org.eclipse.e4.ui.workbench.renderers.swt.HandledContributionItem.handleWidgetSelection(HandledContributionItem.java:743)
at org.eclipse.e4.ui.workbench.renderers.swt.HandledContributionItem.access$7(HandledContributionItem.java:727)
at org.eclipse.e4.ui.workbench.renderers.swt.HandledContributionItem$4.handleEvent(HandledContributionItem.java:662)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4166)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1466)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1489)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1474)
at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:1279)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4012)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3651)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:1113)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:997)
at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:138)
at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:610)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:567)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:150)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:124)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
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:354)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:181)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:636)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:591)
at org.eclipse.equinox.launcher.Main.run(Main.java:1450)