java.lang.ClassCastException: org.eclipse.ui.internal.part.NullEditorInput cannot be cast to org.eclipse.jdt.internal.ui.javaeditor.IClassFileEditorInput
	at org.jboss.tools.maven.sourcelookup.ui.actions.AttachSourcesActionDelegate.setActiveEditor(AttachSourcesActionDelegate.java:79)
	at org.eclipse.ui.internal.EditorPluginAction.editorChanged(EditorPluginAction.java:77)
	at org.eclipse.ui.internal.EditorActionBuilder$EditorContribution.editorChanged(EditorActionBuilder.java:86)
	at org.eclipse.ui.internal.EditorActionBuilder$ExternalContributor.setActiveEditor(EditorActionBuilder.java:135)
	at org.eclipse.ui.internal.EditorActionBars.partChanged(EditorActionBars.java:357)
	at org.eclipse.ui.internal.WorkbenchPage.updateActivations(WorkbenchPage.java:298)
	at org.eclipse.ui.internal.WorkbenchPage.access$17(WorkbenchPage.java:280)
	at org.eclipse.ui.internal.WorkbenchPage$E4PartListener.partActivated(WorkbenchPage.java:202)
	at org.eclipse.e4.ui.internal.workbench.PartServiceImpl$3.run(PartServiceImpl.java:234)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
	at org.eclipse.e4.ui.internal.workbench.PartServiceImpl.firePartActivated(PartServiceImpl.java:231)
	at org.eclipse.e4.ui.internal.workbench.PartServiceImpl.activate(PartServiceImpl.java:682)
	at org.eclipse.e4.ui.internal.workbench.PartServiceImpl.activate(PartServiceImpl.java:613)
	at org.eclipse.e4.ui.internal.workbench.swt.AbstractPartRenderer.activate(AbstractPartRenderer.java:106)
	at org.eclipse.e4.ui.workbench.renderers.swt.StackRenderer$9.handleEvent(StackRenderer.java:1017)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4487)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1388)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1412)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1397)
	at org.eclipse.swt.widgets.Shell.setActiveControl(Shell.java:1714)
	at org.eclipse.swt.widgets.Control.gtk_button_press_event(Control.java:3024)
	at org.eclipse.swt.widgets.Control.gtk_button_press_event(Control.java:2960)
	at org.eclipse.swt.widgets.Composite.gtk_button_press_event(Composite.java:723)
	at org.eclipse.swt.widgets.Widget.windowProc(Widget.java:2077)
	at org.eclipse.swt.widgets.Control.windowProc(Control.java:5510)
	at org.eclipse.swt.widgets.Display.windowProc(Display.java:4701)
	at org.eclipse.swt.internal.gtk.OS._gtk_main_do_event(Native Method)
	at org.eclipse.swt.internal.gtk.OS.gtk_main_do_event(OS.java:9074)
	at org.eclipse.swt.widgets.Display.eventProc(Display.java:1253)
	at org.eclipse.swt.internal.gtk.OS._g_main_context_iteration(Native Method)
	at org.eclipse.swt.internal.gtk.OS.g_main_context_iteration(OS.java:2473)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3439)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:1152)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1033)
	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:382)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:236)
	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)
	at org.eclipse.equinox.launcher.Main.main(Main.java:1438)