[ONOS-4563][ONOS-4564][ONOS-4551][ONOS-4538]defect fix

Change-Id: Ia3fe844e1e846d2e1d2c4359eefc815e7767aef9
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/utils/UtilConstants.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/utils/UtilConstants.java
index c96a6ef..9ca906f 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/utils/UtilConstants.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/utils/UtilConstants.java
@@ -1122,6 +1122,18 @@
             " for YANG utils road map.";
 
     /**
+     * Static attribute for typedef linker error information.
+     */
+    public static final String TYPEDEF_LINKER_ERROR = "YANG file error: Unable to find base "
+            + "typedef for given type";
+
+    /**
+     * Static attribute for grouping linker error information.
+     */
+    public static final String GROUPING_LINKER_ERROR = "YANG file error: Unable to find base "
+            + "grouping for given uses";
+
+    /**
      * Creates an instance of util constants.
      */
     private UtilConstants() {