HHH-7912 - Define edge-case behavior for Session.evict

(cherry picked from commit 0ffe6e7115)

hibernate-core/src/main/java/org/hibernate/engine/internal/EntityEntryContext.java

@@ -1,7 +1,7 @@
 /*
  * Hibernate, Relational Persistence for Idiomatic Java
  *
- * Copyright (c) 2012, Red Hat Inc. or third-party contributors as
+ * Copyright (c) 2013, Red Hat Inc. or third-party contributors as
  * indicated by the @author tags or express copyright attribution
  * statements applied by the authors.  All third-party contributions are
  * distributed under license by Red Hat Inc.
@@ -163,7 +163,7 @@ public class EntityEntryContext {
 		}
 
 		if ( managedEntity == null ) {
-			throw new AssertionFailure( "Unable to resolve entity reference to EntityEntry for removal" );
+			return null;
 		}
 
 		// prepare for re-linking...