What does it mean if you get a blank fortune cookie?

If there is no fortune in a fortune cookie, it is a sign that something good will happen to you soon. (Because fortune-cookie-fairy owes you one fortune.)

Is an empty fortune cookie bad luck?

According to Grub Street Boston “empty fortune cookies belong to the lucky”, but according to Wiki Answers “you may have bad luck for the rest of your life”. urbandictionary.com shows “empty fortune cookie” as an adjective: 1) impotent, 2) a failure at life. including his “final fortune”.