bugfix: added null check

org.fortiss.tooling.kernel/trunk/src/org/fortiss/tooling/kernel/internal/ElementCompositorService.java

@@ -100,6 +100,9 @@ public final class ElementCompositorService extends
 	private IElementCompositor<EObject> findWorkingCompositor(
 			EObject container, EObject contained,
 			IElementCompositionContext context, boolean decompose) {
+		if (container == null) {
+			return null;
+		}
 		List<IElementCompositor<EObject>> list = getRegisteredHandlers(container
 				.getClass());
 		if (list == null) {