Conditional Permissions

I am trying to get a list of Assignees of tasks inside a Project. But I only want this list if it is an “active” project. This in turn drives permissions to Projects and Accounts. The issue that I am running into is that Tasks can have multiple assignments so when trying to place logic to determine if a user should have access I am faced with an error “Can’t use Collections inside IF function”.

Any ideas to get around this? I basically need to create a condition in front of a lookup. The only way that I can think of is to limit assignees to one user, which has other issues.

Try: Assignees.Filter([This Task].State.Final=true). I didn’t test this, but i think it should work