YANG Derived Data Type Support + Change in YANG Parser Grammar to 
Support String values which are not in double quotes with UT case + 
Addition of Revision Date Validation with UT case + Removal of 
String.valueOf

Change-Id: Ic152265a35c0d2b0f84473a94ca67681cf8efca8
diff --git a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/SubModuleListener.java b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/SubModuleListener.java
index 42c753c..b577bcf 100644
--- a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/SubModuleListener.java
+++ b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/SubModuleListener.java
@@ -71,7 +71,7 @@
                                              GeneratedYangParser.SubModuleStatementContext ctx) {
 
         // Check if stack is empty.
-        checkStackIsEmpty(listener, INVALID_HOLDER, SUB_MODULE_DATA, String.valueOf(ctx.IDENTIFIER().getText()),
+        checkStackIsEmpty(listener, INVALID_HOLDER, SUB_MODULE_DATA, ctx.IDENTIFIER().getText(),
                           ENTRY);
 
         YangSubModule yangSubModule = new YangSubModule();
@@ -91,12 +91,12 @@
                                             GeneratedYangParser.SubModuleStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, SUB_MODULE_DATA, String.valueOf(ctx.IDENTIFIER().getText()),
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, SUB_MODULE_DATA, ctx.IDENTIFIER().getText(),
                              EXIT);
 
         if (!(listener.getParsedDataStack().peek() instanceof YangSubModule)) {
             throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, SUB_MODULE_DATA,
-                                                                    String.valueOf(ctx.IDENTIFIER().getText()), EXIT));
+                                                                    ctx.IDENTIFIER().getText(), EXIT));
         }
     }
 }