NPE in saving project properties

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Go to properties of project (Alt+Enter)
2. Go to Google -> App Engine -> Validation
3. Select "Add Multiple..." and add a directory.
4. Press the OK button of the properties view.

You get an error dialog with the message

"An error occured while saving project properties:

null

See the Eclipse error log for more details
"

The log has this exeption:

java.lang.NullPointerException
    at com.google.appengine.eclipse.core.properties.ui.GaeProjectPropertyPage.saveChangesToAppEngineWebXml(GaeProjectPropertyPage.java:890)
    at com.google.appengine.eclipse.core.properties.ui.GaeProjectPropertyPage.saveProjectProperties(GaeProjectPropertyPage.java:336)
    at com.google.gdt.eclipse.core.ui.AbstractProjectPropertyPage.performOk(AbstractProjectPropertyPage.java:77)
    at org.eclipse.jface.preference.PreferenceDialog$13.run(PreferenceDialog.java:965)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
    at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:49)
    at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:175)
    at org.eclipse.jface.preference.PreferenceDialog.okPressed(PreferenceDialog.java:945)
    at org.eclipse.ui.internal.dialogs.FilteredPreferenceDialog.okPressed(FilteredPreferenceDialog.java:448)
    at org.eclipse.jface.preference.PreferenceDialog.buttonPressed(PreferenceDialog.java:233)
    at org.eclipse.jface.dialogs.Dialog$2.widgetSelected(Dialog.java:628)
    at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:248)
    at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1057)
    at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4170)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3759)
    at org.eclipse.jface.window.Window.runEventLoop(Window.java:826)
    at org.eclipse.jface.window.Window.open(Window.java:802)
    at org.eclipse.ui.dialogs.PropertyDialogAction.run(PropertyDialogAction.java:158)
    at org.eclipse.jface.action.Action.runWithEvent(Action.java:499)
    at org.eclipse.jface.action.ActionContributionItem.handleWidgetSelection(ActionContributionItem.java:584)
    at org.eclipse.jface.action.ActionContributionItem.access$2(ActionContributionItem.java:501)
    at org.eclipse.jface.action.ActionContributionItem$5.handleEvent(ActionContributionItem.java:411)
    at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1057)
    at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4170)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3759)
    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:140)
    at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:611)
    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(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    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)
    at org.eclipse.equinox.launcher.Main.main(Main.java:1426)

The project ha no GWT nor AppEngine enabled but I am still able to add 
validation excludes which cause the above NPE.

I expect to not be able to add anything when the project is not enabled for GWT 
nor App Engine.

What version of the product are you using? On what operating system?

This is my session data:

eclipse.buildId=4.3.2.M20140221-1700
java.version=1.7.0_40
java.vendor=Oracle Corporation
BootLoader constants: OS=win32, ARCH=x86_64, WS=win32, NL=de_DE
Command-line arguments:  -os win32 -ws win32 -arch x86_64

Original issue reported on code.google.com by udo.wal...@abas.de on 8 Apr 2014 at 8:46

[GoogleCodeExporter]

Do you have an appengine-web.xml file under war/WEB-INF/lib?

Original comment by rdayal@google.com on 12 May 2014 at 6:28

[GoogleCodeExporter]

No, I do not use the appengine at all.

Original comment by udo.wal...@abas.de on 13 May 2014 at 7:20

[GoogleCodeExporter]

Got it. Sounds like we need to be disabling these property pages whenever GAE 
is not enabled. 

Original comment by rdayal@google.com on 27 Jun 2014 at 2:58