ICompilationUnit#findPrimaryType()がnullになり、
以下のようにNullPointerExceptionが発生する。

java.lang.NullPointerException
at org.seasar.sastrutsplugin.util.IDEUtil.openEditor(IDEUtil.java:79)
at org.seasar.sastrutsplugin.util.IDEUtil.openEditor(IDEUtil.java:61)
at org.seasar.sastrutsplugin.action.OpenJavaAction.run(OpenJavaAction.java:130)
at org.eclipse.ui.internal.handlers.ActionDelegateHandlerProxy.execute(ActionDelegateHandlerProxy.java:271)
at org.eclipse.core.commands.Command.executeWithChecks(Command.java:475)
at org.eclipse.core.commands.ParameterizedCommand.executeWithChecks(ParameterizedCommand.java:429)
at org.eclipse.ui.internal.handlers.HandlerService.executeCommand(HandlerService.java:165)
at org.eclipse.ui.internal.keys.WorkbenchKeyboard.executeCommand(WorkbenchKeyboard.java:470)
at org.eclipse.ui.internal.keys.WorkbenchKeyboard.press(WorkbenchKeyboard.java:821)
at org.eclipse.ui.internal.keys.WorkbenchKeyboard.processKeyEvent(WorkbenchKeyboard.java:879)
at org.eclipse.ui.internal.keys.WorkbenchKeyboard.filterKeySequenceBindings(WorkbenchKeyboard.java:568)
at org.eclipse.ui.internal.keys.WorkbenchKeyboard.access$3(WorkbenchKeyboard.java:510)
at org.eclipse.ui.internal.keys.WorkbenchKeyboard$KeyDownFilter.handleEvent(WorkbenchKeyboard.java:126)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:66)
at org.eclipse.swt.widgets.Display.filterEvent(Display.java:1141)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:937)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:962)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:947)
at org.eclipse.swt.widgets.Widget.sendKeyEvent(Widget.java:975)
at org.eclipse.swt.widgets.Widget.sendKeyEvent(Widget.java:971)
at org.eclipse.swt.widgets.Widget.wmKeyDown(Widget.java:1570)
at org.eclipse.swt.widgets.Control.WM_KEYDOWN(Control.java:3992)
at org.eclipse.swt.widgets.Control.windowProc(Control.java:3701)
at org.eclipse.swt.widgets.Canvas.windowProc(Canvas.java:291)
at org.eclipse.swt.widgets.Display.windowProc(Display.java:4364)
at org.eclipse.swt.internal.win32.OS.DispatchMessageW(Native Method)
at org.eclipse.swt.internal.win32.OS.DispatchMessage(OS.java:2265)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3291)
at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2389)
at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2353)
at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2219)
at org.eclipse.ui.internal.Workbench$4.run(Workbench.java:466)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:289)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:461)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:106)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:169)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:106)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:76)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:363)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:176)
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:585)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:508)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:447)
at org.eclipse.equinox.launcher.Main.run(Main.java:1173)
at org.eclipse.equinox.launcher.Main.main(Main.java:1148)