When Card visual with filters is BLANK replace with Text

I am using a card visual to show text from column called [Subject] from table Append1. 
I have a filter on the card visual to only show when another column [Area] from table Append1 is a specific value. So as expected the card will sometimes show (Blank). I want to replace the blank with text "Free", I have tried to put this in a measure but it isn't working. Please help!