Custome Adapter Module in Receiver channel

Hi All,

I am developed  new custom adapter module  and I want it to be called after the execution standard module in File receiver channel.

But I am getting a Null pointer exception as it has lost the reference to ModuleData while the custom module is invoked.

*****Error message

Transmitting the message to endpoint <local> using connection File_http://sap.com/xi/XI/System failed, due to: com.sap.engine.interfaces.messaging.api.exception.MessagingException: java.lang.NullPointerException: while trying to invoke the method com.sap.engine.interfaces.messaging.api.Message.getMessageId() of a null object loaded from local variable msg

********

But When the same module is placed before standard "CallSapAdapter", it is getting executed successfully.

Could some please advise if we can call a custom module after standard Sap "CallSapAdapter" module.

Part code:

obj =  inputModuleData.getPrincipalData();

msg = (Message)obj;           

loc = Location.getLocation(getClass().getName());

this.trace = moduleContext.getContextData("trace");

this.key = new MessageKey(msg.getMessageId(), msg.getMessageDirection());

Getting error @this.key = new MessageKey(msg.getMessageId(), msg.getMessageDirection()); as msg object is null.