Translator Override + (add) property button should not be enabled unless Override Translator is selected

Because the add property button is enabled, without selecting an Overridden translator, pressing it causes:

java.lang.NullPointerException
at org.teiid.designer.vdb.ui.translators.TranslatorOverridesPanel.handleAddProperty(TranslatorOverridesPanel.java:521)
at org.teiid.designer.vdb.ui.translators.TranslatorOverridesPanel$14.widgetSelected(TranslatorOverridesPanel.java:424)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:248)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)