Fix bug during creation of edges

Change-Id: Ibe3612c52fefa09ef8813c0b411002b3c7af1f71
diff --git a/plugins/org.eclipse.emf.henshin.model/src/org/eclipse/emf/henshin/model/impl/RuleImpl.java b/plugins/org.eclipse.emf.henshin.model/src/org/eclipse/emf/henshin/model/impl/RuleImpl.java
index ba27ef1..ccb05c1 100644
--- a/plugins/org.eclipse.emf.henshin.model/src/org/eclipse/emf/henshin/model/impl/RuleImpl.java
+++ b/plugins/org.eclipse.emf.henshin.model/src/org/eclipse/emf/henshin/model/impl/RuleImpl.java
@@ -825,7 +825,8 @@
 	
 
 	private boolean forbidEdgeExists(Node source, Node target, EReference type) {
-		if (source.getAction().getType() != Action.Type.PRESERVE &&
+		if (source.getAction() == null || target.getAction() == null || 
+				source.getAction().getType() != Action.Type.PRESERVE &&
 				target.getAction().getType() != Action.Type.PRESERVE)
 			return false;