Autocomplete Validation Rule - To check the number of times the assignment change is done and show t

Content

The requirement is in the Confirmation Process Screen. The underlying assignment change action is Working Hours Change. The action reasons available are Confirm, Extend and Initiate Exit. The requirement is that unless and until the assignment change happened twice with action reason as Extend, they are not allowed to select Initiate Exit reason. For this we are using Loop Back row. But I'm getting an error that cannot trigger null at line number 24. I have uploaded the AutoComplete Rule and also the error message screenshots.