How to retrieve repeating groups from the FIX messages using quickfixj library?

Question

I have been referring to the quickfixj documentation which states, one can retrieve the repeating groups as given here: https://www.quickfixj.org/usermanual/2.3.0/usage/repeating_groups.html. But the given approach is not working in the acceptor, though it is able to extract the repeating groups, when parsed in the sender itself. On trying to fetch the repeating groups, it gives the fails with the Exception : "Method threw, Quickfix.FieldNotFoundException". Kindly suggest on the same.

// FIX50SP2.modified.xml for adding custom message 

<!--In the message declaration section--->
<value enum="CZ" description="MYSAMPLEMESSAGE"/>

    enter code here

<!--In the message definition section--->
<message name="MySampleMessage" msgtype="CZ" msgcat="app">
<field name="EntitlementRepId" required="Y"/>
<component name="EntitlementUpdateGrp" required="Y"/>
<field name="Text" required="N"/>
</message>

<!--In the component definition section--->
<component name="EntitlementUpdateGrp">
 <group name="NoPartyEntitlements" required="Y">
   <field name="ListUpdateAction" required="Y"/>
 </group>
</component>

<!--In the field declaration section--->
<field number="1771" name="EntitlementRepId" type="STRING"/>
<field number="1772" name="NoPartyEntitlements" type="NUMINGROUP"/>
 


public class Acceptor extends MessageCracker implements Application{


    public void onMessage(MySampleMessage message,SessionID sessionId)throws Exception
    {
        MySampleMessage.NoPartEntitlements noPartyEntitlements=new MySampleMessage.NoPartEntitlements();
        ListUpdateAction listUpdateAction=new ListUpdateAction();
        message.getGroup(1,noPartyEntitlements);//FieldNotFound Exception is thrown

    }

    @override
    public void fromApp(Message message,SessionID sessionId)throws Exception
    {
       crack(message,sessionId);
    }


}