Evaluating Oracle Null Date in Crystal

I am using Crystal Reports in Visual Studio 2003.
I am unable to evaluate a null date/time in a formula field. All I want to do is :
If date is null
then “No”
else “Yes”;
My unsuccessful attempts :
1. “Is Null” errors out looking for a “Then” even though I have one.
2. I tried converting the date to text and checking if it’s length > 0.