NPE when closing OSATE

[lwrage]

Summary

When running OSATE from the development environment I often get a null pointer exception when terminating OSATE.

Stack trace

java.lang.NullPointerException
	at org.osate.ui.navigator.ViewerRefresher.lambda$0(ViewerRefresher.java:57)
	at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:40)
	at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:185)
	at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:4910)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:4432)
	at org.eclipse.jface.operation.ModalContext$ModalContextThread.block(ModalContext.java:166)
	at org.eclipse.jface.operation.ModalContext.run(ModalContext.java:368)
	at org.eclipse.jface.dialogs.ProgressMonitorDialog.run(ProgressMonitorDialog.java:469)
(... snip ...)

Environment

• OSATE Version: 2.7.0 nightly
• Operating System: Linux