I too was looking for the catch. So I looked up the command in the help, just to make sure I wasn't forgetting about something obscure. Nothing weird, so I opened a query window in SQL 2005 and pasted it in. Still not believing it was that simple, I clicked Execute and got an error message stating that it couldn't find the stored procedure ISNULL. WTF There is a catch, but what is it!
After I cleared the line and re-entered it, it responded with the correct answer of 1.
What! I redid the original Paste, but it only responds with the correct answer. I really wanted to paste the error here, but I can't get it to repeat.
God I love computers!