Bug 520764 - MaterializingBackwardConverter.resolveLiteral does not
handle null correctly

* allow null

Change-Id: Ie1a160f5a5e8687f997c5774a102edac8f1b20bd
Signed-off-by: Johannes Faltermeier <jfaltermeier@eclipsesource.com>
diff --git a/plugins/org.eclipse.emf.edapt.migration/src/org/eclipse/emf/edapt/internal/migration/internal/MaterializingBackwardConverter.java b/plugins/org.eclipse.emf.edapt.migration/src/org/eclipse/emf/edapt/internal/migration/internal/MaterializingBackwardConverter.java
index 23f1929..fe6276c 100644
--- a/plugins/org.eclipse.emf.edapt.migration/src/org/eclipse/emf/edapt/internal/migration/internal/MaterializingBackwardConverter.java
+++ b/plugins/org.eclipse.emf.edapt.migration/src/org/eclipse/emf/edapt/internal/migration/internal/MaterializingBackwardConverter.java
@@ -56,6 +56,8 @@
 				.createFromString(targetEnum, value);
 		} else if (Enumerator.class.isInstance(literal)) {
 			return Enumerator.class.cast(literal);
+		} else if (literal == null) {
+			return null;
 		}
 		throw new IllegalArgumentException(MessageFormat.format(
 			"Unexpected literal {0} of type {1} cannot be converted to an Enumerator", literal, literal.getClass())); //$NON-NLS-1$