TCI - Fix possible NPE

Change-Id: Ia82f33c9d02f814b6ef8d4caba1b8628a9cb15e3
Signed-off-by: Eugen Neufeld <eneufeld@eclipsesource.com>
diff --git a/bundles/org.eclipse.emf.ecp.view.core.swt/src/org/eclipse/emf/ecp/view/internal/core/swt/renderer/EnumComboViewerSWTRenderer.java b/bundles/org.eclipse.emf.ecp.view.core.swt/src/org/eclipse/emf/ecp/view/internal/core/swt/renderer/EnumComboViewerSWTRenderer.java
index ad6534b..5f32645 100644
--- a/bundles/org.eclipse.emf.ecp.view.core.swt/src/org/eclipse/emf/ecp/view/internal/core/swt/renderer/EnumComboViewerSWTRenderer.java
+++ b/bundles/org.eclipse.emf.ecp.view.core.swt/src/org/eclipse/emf/ecp/view/internal/core/swt/renderer/EnumComboViewerSWTRenderer.java
@@ -244,7 +244,9 @@
 
 	@Override
 	protected void rootDomainModelChanged() throws DatabindingFailedException {
-		availableChoicesValue.dispose();
+		if (availableChoicesValue != null) {
+			availableChoicesValue.dispose();
+		}
 		availableChoicesValue = null;
 		super.rootDomainModelChanged();
 	}