fixed validation for reference update op: was missing the either HashedObject or pure javascript literal part!

Author: sbazerque

src/data/collections/mutable/MutableReference.ts

@@ -190,10 +190,17 @@ class RefUpdateOp<T> extends CollectionOp<T> {
         }
 
         if (this.value === undefined) {
-            MutableObject.validationLog.debug('The field value is mandatory in class REfUpdateop');
+            MutableObject.validationLog.debug('The field value is mandatory in class RefUpdateop');
             return false;
         }
 
+        if (!(this.value instanceof HashedObject)) {
+            if (!HashedObject.isLiteral(this.value)) {
+                MutableObject.validationLog.debug('The field value in class RefUpdateop must either be a HashedObject instance or a pure literal (a constant, without any HashedObjects within).');
+                return false;
+            }
+        }
+
         return true;
     }