Error processing Resultset in Execute Stored Procedure - SQL Server

We are using Execute Stored Procedure to execute DB operations. we are facing issues in retrieving the resultset in case an output parameter is defined in the procedure.

Definition - @ErrorMessage varchar(4000) output

The Procedure is for get operation and below are the observations :

fn!executestoredprocedure :  The resultset is not returned

O/p - [success:false,error:Error processing results in procedure XXXXX ]

Smart Service : The smart service node errors out with an alert for null pointer.

Alert : There is a problem with task “Execute Stored Procedure” in the process “XXXXXX”. java.lang.NullPointerException
Problem:  An error occurred in executing an Activity Class.  


* These issues are resolved and the resultset is properly populated if we remove the Output param mapped in the procedure.
* Even a declaration of output param is good enough to break the call i.e no processing just a standard declaration.
* If I don't attempt retrieving the resultset, even with parameters declared the smart service executes (doesn't throw null pointer exception).