Fix error - object reference not set to an instance of an object c#

I am using a D365 plugin to update values in the event of record creation and updation. The values are getting updated for "create" event but not for "update" event - giving an error message "object reference not set to an instance of an object"
Please respond urgently if interested, I will then send you the .cs file.
Appreciate your help to fix the issue.

Thanks