I want to evaluate a workflow rule based on a custom setting value. The custom setting can be null so I want to check for isNULL before fetching the value of the custom settings field.
This is the formula I'm using
AND(ISPICKVAL(Rating, "Closed Won"), ISNULL($Setup.MySettings__c.notify__c))
This, however, returns a syntax error - "Error: Incorrect argument type for function 'ISNULL()'."
Is there any other way to check for Blank or null values for custom settings?