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/ImportListener.java b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ImportListener.java
index e47f466..1f5e113 100644
--- a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ImportListener.java
+++ b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ImportListener.java
@@ -75,10 +75,10 @@
     public static void processImportEntry(TreeWalkListener listener, GeneratedYangParser.ImportStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, IMPORT_DATA, String.valueOf(ctx.IDENTIFIER().getText()), ENTRY);
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, IMPORT_DATA, ctx.IDENTIFIER().getText(), ENTRY);
 
         YangImport importNode = new YangImport();
-        importNode.setModuleName(String.valueOf(ctx.IDENTIFIER().getText()));
+        importNode.setModuleName(ctx.IDENTIFIER().getText());
 
         // Push import node to the stack.
         listener.getParsedDataStack().push(importNode);
@@ -94,14 +94,14 @@
     public static void processImportExit(TreeWalkListener listener, GeneratedYangParser.ImportStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, IMPORT_DATA, String.valueOf(ctx.IDENTIFIER().getText()), EXIT);
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, IMPORT_DATA, ctx.IDENTIFIER().getText(), EXIT);
 
         Parsable tmpImportNode = listener.getParsedDataStack().peek();
         if (tmpImportNode instanceof YangImport) {
             listener.getParsedDataStack().pop();
 
             // Check for stack to be non empty.
-            checkStackIsNotEmpty(listener, MISSING_HOLDER, IMPORT_DATA, String.valueOf(ctx.IDENTIFIER().getText()),
+            checkStackIsNotEmpty(listener, MISSING_HOLDER, IMPORT_DATA, ctx.IDENTIFIER().getText(),
                                  EXIT);
 
             Parsable tmpNode = listener.getParsedDataStack().peek();
@@ -118,12 +118,12 @@
             }
             default:
                 throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, IMPORT_DATA,
-                                                                        String.valueOf(ctx.IDENTIFIER().getText()),
+                                                                        ctx.IDENTIFIER().getText(),
                                                                         EXIT));
             }
         } else {
             throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, IMPORT_DATA,
-                                                                    String.valueOf(ctx.IDENTIFIER().getText()), EXIT));
+                                                                    ctx.IDENTIFIER().getText(), EXIT));
         }
     }
 }