Hello Tableau Community!

I need to replace integer nulls from a Measure's Calc Field in my view with a string.

For example I want The Number of Days to Close Calc Field in the print screen below to show 'Case Open' when a null is found in the Calc Filed below

•      In other words, when there is a null how do I change that null to say 'Case Open'?
•      DATEDIFF('day',[Created Date GMT],[CLOSEDDATE_GMT],'Sunday')

My Calc Field started off in the Measure's Shelf, until I changed its data type to a string and is now in the.

Calc Field when in Measure's Shelf  (*Before my attempt to change Nulls to a string)

DATEDIFF('day',[Created Date GMT],[CLOSEDDATE_GMT],'Sunday')

Calc Field when in Dimension' Shelf  (*After my attempt to change Nulls to a string)

IF ISNULL(DATEDIFF('day',[Created Date GMT],[CLOSEDDATE_GMT],'Sunday'))

THEN 'Open' ELSE STR(DATEDIFF('day',[Created Date GMT],[CLOSEDDATE_GMT],'Sunday'))

END

I reviewed Can I replace "Null Values" with a string ? and other documents but could not find my answer.

Thank you for your help.

-Manuel