Are there any conventions around closing an account with a credit balance?

I'm working with a site with member accounts. Those accounts can have credits attached (say from a referral incentive, a voucher, or a prize). The credits can then be spent in the site's shop - they're a dollar value in the same currency the site uses.

I am wondering how to handle a user closing their account while it is still in credit - what will users expect to happen?

I can think of two possible solutions:

  1. Warn the user that closing their account will forfeit their credit (throw their credit away) Obviously the simplest, but I wonder if it's too unfriendly.
  2. Don't allow the user to close their account while it has a credit balance (make them spend it). I think this is a non-starter because the balance may be too low to actually buy anything outright, which would mean that they'd need to spend their own money to close their account.

Am I missing anything? What would you expect to happen in this situation?

There are a lot of great responses to this question below. I've accepted one that suits my situation, but others would be very viable on different sites/services.