NullPointerException if "module" statement is removed (or entire contents) after setting selection

[davidmichaelkarr]

It's an odd test case, but I usually can repeat this sequence:

1. While viewing a valid Yang file, select some text in the buffer.
2. Select entire buffer.
3. Press Delete to empty buffer.

This will often result in the following stacktrace:

java.lang.NullPointerException
    at com.cisco.yangide.editor.editors.YangEditor$YangEditorSelectionChangedListener.selectionChanged(YangEditor.java:154)
    at org.eclipse.jface.text.TextViewer.firePostSelectionChanged(TextViewer.java:2751)
    at org.eclipse.jface.text.TextViewer.firePostSelectionChanged(TextViewer.java:2699)
    at org.eclipse.jface.text.TextViewer$5.run(TextViewer.java:2678)
    at org.eclipse.swt.widgets.Display.timerProc(Display.java:4406)
    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:2425)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3428)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$4.run(PartRenderingEngine.java:1127)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:337)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1018)
    at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:156)
    at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:654)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:337)
    at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:598)
    at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:150)
    at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:139)
    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:380)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:235)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:669)
    at org.eclipse.equinox.launcher.Main.basicRun(Main.java:608)
    at org.eclipse.equinox.launcher.Main.run(Main.java:1515)
    at org.eclipse.equinox.launcher.Main.main(Main.java:1488)

Here is the method in question at the top of stack:

    private class YangEditorSelectionChangedListener extends AbstractSelectionChangedListener {

        @Override
        public void selectionChanged(SelectionChangedEvent event) {
            if (event.getSelection() instanceof ITextSelection) {
                ITextSelection textSelection = (ITextSelection) event.getSelection();
                try {
                    if (null != outlinePage) { // next line is line 154
                        outlinePage.selectNode(getModule().getNodeAtPosition(textSelection.getOffset()));
                    }
                } catch (YangModelException e) {
                }
            }

        }
    }

From debugging, I found that "getModule()" returns null in this situation, although there also appears to be a race condition in play that I don't clearly understand. I tried adding an "if" specifically for "getModule() == null" before the "if" on line 153, with a print statement saying that "getModule()" returned null. I set a breakpoint there, and when I hit that, I executed "getModule()" in the display view, and it gave me a non-null value.

It seems safe to amend the "if" condition on line 153, adding "null != getModule()". A brief comment about this situation before the "if" would be beneficial also.