Date validation: Cannot read property "DUE_DATE"

I am trying to do date validation.Two fileds are involved here one is in-build "Due date" and the second is the custom field extended date. But when the script is triggered i get the below error:

!ENTRY com.ibm.team.workitem.common 4 0 2016-06-09 19:31:57.154
!MESSAGE Error invoking validator com.ibm.team.workitem.valueproviders.VALIDATOR._e6trIC4oEeaDz9yQi8uE-Q
!STACK 0
com.ibm.team.repository.common.TeamRepositoryException: Unexpected exception type
 at com.ibm.team.workitem.shared.common.internal.valueProviders.ScriptAttributeValueProvider.handleException(ScriptAttributeValueProvider.java:281)
 at com.ibm.team.workitem.shared.common.internal.valueProviders.ScriptAttributeValueProvider.validate(ScriptAttributeValueProvider.java:149)
 at com.ibm.team.workitem.common.internal.attributeValueProviders.AttributeValueProviderRegistry$SafeValidator.validate(AttributeValueProviderRegistry.java:152)
 at com.ibm.team.workitem.common.internal.model.impl.AttributeImpl.validate(AttributeImpl.java:928)
 at sun.reflect.GeneratedMethodAccessor108.invoke(Unknown Source)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37)
 at java.lang.reflect.Method.invoke(Method.java:611)
 at com.ibm.team.repository.common.internal.util.ItemStore$ItemInvocationHandler.invoke(ItemStore.java:597)
 at com.sun.proxy.$Proxy41.validate(Unknown Source)
 at com.ibm.team.workitem.client.internal.util.WorkItemEventResolver$InternalBackgroundJob.resolve(WorkItemEventResolver.java:261)
 at com.ibm.team.workitem.client.internal.util.WorkItemEventResolver$InternalBackgroundJob.runProtected(WorkItemEventResolver.java:89)
 at com.ibm.team.foundation.client.util.FoundationJob.run(FoundationJob.java:68)
 at org.eclipse.core.internal.jobs.Worker.run(Worker.java:53)
Caused by: org.mozilla.javascript.EcmaError: TypeError: Cannot read property "DUE_DATE" from undefined (date-validator.js#24)
 at org.mozilla.javascript.ScriptRuntime.constructError(ScriptRuntime.java:3557)
 at org.mozilla.javascript.ScriptRuntime.constructError(ScriptRuntime.java:3535)
 at org.mozilla.javascript.ScriptRuntime.typeError(ScriptRuntime.java:3563)
 at org.mozilla.javascript.ScriptRuntime.typeError2(ScriptRuntime.java:3582)
 at org.mozilla.javascript.ScriptRuntime.undefReadError(ScriptRuntime.java:3595)
 at org.mozilla.javascript.ScriptRuntime.getObjectProp(ScriptRuntime.java:1381)
 at org.mozilla.javascript.gen.c19._c2(date-validator.js:24)
 at org.mozilla.javascript.gen.c19.call(date-validator.js)
 at org.mozilla.javascript.ContextFactory.doTopCall(ContextFactory.java:401)
 at org.mozilla.javascript.ScriptRuntime.doTopCall(ScriptRuntime.java:3003)
 at org.mozilla.javascript.gen.c19.call(date-validator.js)
 at com.ibm.team.rtc.common.scriptengine.internal.bridge.proxy.AbstractInvocationHandler$MethodHandler$1.run(AbstractInvocationHandler.java:160)
 at com.ibm.team.rtc.common.scriptengine.environment.AbstractScriptEnvironment.execute(AbstractScriptEnvironment.java:74)
 at com.ibm.team.rtc.common.scriptengine.internal.bridge.proxy.AbstractInvocationHandler$MethodHandler.invoke(AbstractInvocationHandler.java:156)
 at com.ibm.team.rtc.common.scriptengine.internal.bridge.proxy.AbstractInvocationHandler.invokeGeneric(AbstractInvocationHandler.java:141)
 at com.ibm.team.rtc.common.scriptengine.internal.bridge.proxy.AbstractInvocationHandler.invoke(AbstractInvocationHandler.java:95)
 at com.sun.proxy.$Proxy55.validate(Unknown Source)
 at com.ibm.team.workitem.shared.common.internal.valueProviders.ScriptAttributeValueProvider.validate(ScriptAttributeValueProvider.java:147)
 ... 11 more

Below is my javascriot code for the same. --

dojo.provide("org.example.DateValidator");

dojo.require("com.ibm.team.workitem.api.common.Severity");
dojo.require("com.ibm.team.workitem.api.common.Status");
dojo.require("dojo.date"); // We need the date class from Dojo to compare two dates
dojo.require("dojo.date.stamp"); // We need the stamp class to work with ISO date strings

(function() {
var Severity = com.ibm.team.workitem.api.common.Severity;
var Status = com.ibm.team.workitem.api.common.Status;
var WorkItemAttributes = com.ibm.team.workitem.api.common.WorkItemAttributes;
var DateValidator = dojo.declare("org.example.DateValidator", null, {

    validate: function(attributeId, workItem, configuration) {
         console.log("hi");
        // Get the configuration parameters about the severity and error message of this validator
        var severity= configuration.getChild("parameters").getStringDefault("severity", Severity.ERROR.name);
        var message= configuration.getChild("parameters").getStringDefault("message", "");
        console.log(message);
        // Get the Due date attribute
  var dateRequiredBy=dojo.date.stamp.fromISOString(workItem.getValue(WorkItemAttributes.DUE_DATE));

         // Get the current attribute's value and make a Date object from it
  var extendedDate=dojo.date.stamp.fromISOString(workItem.getValue(attributeId));
        console.log(dateRequiredBy);
  console.log(extendedDate);
  // Compare the two dates and make sure extendedDate is not earlier than dateRequiredBy
  //If the dateRequiredBy > extendedDate = +ve else -ve
        if (dojo.date.compare(dateRequiredBy, extendedDate) <= 0) {
            return Status.OK_STATUS;
        } else {
            return new Status(Severity[severity], message);
        }
    }
});
})();

The above code was workin fine in RTC version 3.0.1. recently i have upgraded to RTC 4.0.3 and the script does't work here. WorkItemAttributes.DUE_DATE is not supported or changed in RTC 4.0.3

Please advice what is the issue here ?

Thanks