Action returns object reference error every time i run the action on button click, debuging doesnt show any error, it sets the return values without any issue.

The code i debugged from jscript to Action c3 code, no error is shown, it assigns the resultant value back to output parameter and javascripts expects the values, but it always cause into errorcallbacl with OOB DLL error message 

Starting sync workflow
'Action For Clawback', Id: b4953e91-5cb2-eb11-8148-000c292bd2f2\r\nEntering CustomActivityStep2_step:
Call the WF action for Clawback\r\nSync workflow 'Action For Clawback' terminated with error 'Object reference not set to an instance of an object.'\r\n"