[ONOS-4650][ONOS-4726][ONOS-4727] [ONOS-4728]Implement must parser + when parser + feature + if-feature + revision defect fix

Change-Id: I0a3aee6c1c6b72ef7da7f7f565fd0f149fe3fd42
diff --git a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/utils/UtilConstants.java b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/utils/UtilConstants.java
index 37b8992..f4999b6 100644
--- a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/utils/UtilConstants.java
+++ b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/utils/UtilConstants.java
@@ -1140,6 +1140,12 @@
             + "grouping for given uses";
 
     /**
+     * Static attribute for grouping linker error information.
+     */
+    public static final String FEATURE_LINKER_ERROR = "YANG file error: Unable to find feature "
+            + "for given if-feature";
+
+    /**
      * Static attribute for reference.
      */
     public static final String REFERENCE = "Reference";