I try to clean up an attributetable using calculate field and arcade, some records have their creator in a column 'creator_1' instead of creator so I wrote:
IIf(IsEmpty($feature.Creator),$feature.Creator_1,$feature.Creator)
But all I get is: Invalid expression. error on line 1. Open parenthesis expected

I've looked at the arcade reference and other sources I could think of but I can't see what i'm doing wrong. ArcGIS PRO 2.5.1
your help would be appreciated!
regards,
Bert