[ONOS-4910, ONOS-4921] Framework: utils validation and defect fix

Change-Id: I821920fa8c88e64406b702c2b8736bdeaf231474
diff --git a/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangLeaf.java b/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangLeaf.java
index b01ff63..3060fd4 100644
--- a/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangLeaf.java
+++ b/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangLeaf.java
@@ -380,8 +380,9 @@
     @Override
     public void validateDataOnExit()
             throws DataModelException {
-        // TODO auto-generated method stub, to be implemented by parser
-
+        if (defaultValueInString != null && !defaultValueInString.isEmpty() && dataType != null) {
+            dataType.isValidValue(defaultValueInString);
+        }
     }
 
     @Override