ISSUEWhen a task is assigned to a user using the UPN account property, the following error might occur:
Nintex.Workflow.NWActionExecutionException: Error in task. ---> System.NullReferenceException: Object reference not set to an instance of an object.
RESOLUTIONIn environments where the UPN property is being used as the primary ID, it should be converted into a domain\username property in a workflow first before then using this to assign a task.
ADDITIONAL INFORMATIONThe UPN property is primarily used in environments where user accounts cross multiple domains. This is problematic for the workflow engine, which will struggle to recognise the user account and assign tasks correctly.
User Name Formats in Microsoft Developer Network.