Sadly this issue doesn't always happen. Some defensive code at the NPE site should take care of it.
Occurs sporadically on Disconnect from a specifically attached JMX server

!ENTRY org.eclipse.e4.ui.workbench 4 0 2014-05-22 14:19:37.776
!MESSAGE
!STACK 0
java.lang.NullPointerException
at org.jboss.tools.jmx.ui.internal.editors.AttributeDetails.dispose(AttributeDetails.java:173)
at org.eclipse.ui.forms.DetailsPart$PageBag.dispose(DetailsPart.java:65)
at org.eclipse.ui.forms.DetailsPart.dispose(DetailsPart.java:149)
at org.eclipse.ui.forms.ManagedForm.dispose(ManagedForm.java:174)
at org.eclipse.ui.forms.editor.FormPage.dispose(FormPage.java:178)
at org.eclipse.ui.forms.editor.FormEditor.dispose(FormEditor.java:403)
at org.eclipse.ui.internal.e4.compatibility.CompatibilityPart.invalidate(CompatibilityPart.java:221)
at org.eclipse.ui.internal.e4.compatibility.CompatibilityPart.destroy(CompatibilityPart.java:369)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:56)
at org.eclipse.e4.core.internal.di.InjectorImpl.processAnnotated(InjectorImpl.java:888)
at org.eclipse.e4.core.internal.di.InjectorImpl.processAnnotated(InjectorImpl.java:869)
at org.eclipse.e4.core.internal.di.InjectorImpl.uninject(InjectorImpl.java:180)
at org.eclipse.e4.core.internal.di.Requestor.uninject(Requestor.java:142)
at org.eclipse.e4.core.internal.contexts.ContextObjectSupplier$ContextInjectionListener.update(ContextObjectSupplier.java:82)
at org.eclipse.e4.core.internal.contexts.TrackableComputationExt.update(TrackableComputationExt.java:107)
at org.eclipse.e4.core.internal.contexts.EclipseContext.removeListenersTo(EclipseContext.java:460)
at org.eclipse.e4.core.contexts.ContextInjectionFactory.uninject(ContextInjectionFactory.java:144)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeRemoveGui(PartRenderingEngine.java:917)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.access$3(PartRenderingEngine.java:837)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$8.run(PartRenderingEngine.java:832)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.removeGui(PartRenderingEngine.java:817)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$1.handleEvent(PartRenderingEngine.java:154)
at org.eclipse.e4.ui.services.internal.events.UIEventHandler$1.run(UIEventHandler.java:41)
at org.eclipse.swt.widgets.Synchronizer.syncExec(Synchronizer.java:187)
at org.eclipse.ui.internal.UISynchronizer.syncExec(UISynchronizer.java:150)
at org.eclipse.swt.widgets.Display.syncExec(Display.java:4561)
at org.eclipse.e4.ui.internal.workbench.swt.E4Application$1.syncExec(E4Application.java:210)
at org.eclipse.e4.ui.services.internal.events.UIEventHandler.handleEvent(UIEventHandler.java:38)
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:80)
at org.eclipse.e4.ui.internal.workbench.UIEventPublisher.notifyChanged(UIEventPublisher.java:58)
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:1232)
at org.eclipse.ui.internal.WorkbenchPage.hidePart(WorkbenchPage.java:1501)
at org.eclipse.ui.internal.WorkbenchPage.hidePart(WorkbenchPage.java:1452)
at org.eclipse.ui.internal.WorkbenchPage.closeEditors(WorkbenchPage.java:1422)
at org.eclipse.ui.internal.WorkbenchPage.closeEditor(WorkbenchPage.java:1546)
at org.jboss.tools.jmx.ui.internal.editors.EditorConnectionMapping$1.run(EditorConnectionMapping.java:54)
at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:35)
at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:136)
at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:3748)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3396)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:1122)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1006)
at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:147)
at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:630)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:574)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:150)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:125)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:133)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:103)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:378)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:232)
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:1462)
at org.eclipse.equinox.launcher.Main.main(Main.java:1438)