Subclassing NSFetchedResultsController

Question

I'm trying to use this RichFetchedResultsController, a subclass of NSFetchedResultsController from this blog post. Prior to using this subclass, my codebase have a heavy use of object(at:).

Now I have Xcode giving me these errors:

value of type 'NSFetchRequestResult' has no member 'RelationshipEntityProperty'

I have code written like this

let randomEntity = fetchedResultsController.object(at: indexPath).relationshipEntity

So these are where the errors are showing.

I tried to do this in the subclass of RichFetchedResultsController taken from here and it didn't help:

public override func object(at indexPath: IndexPath) -> NSFetchRequestResult {
    super.object(at: indexPath)
}

Any ideas?