<now someone trades 900 shares for an absolute Zero stock price!>
Likely, establishing a date for tax purposes.
Unfortunately, I've had a few stocks go BK and I sell via a broker to establish a date for tax purposes. Otherwise, the court proceedings could languish for a year or more. If you want the tax losses this year it would be wise to sell to your broker. My broker (TD Ameritrade, in my examples) would buy my entire position for $.01. I'm not sure all brokers do this...
I suppose if anyone were silly enough to still be short the stock, they could also buy the stock back to establish a date for tax purposes as well.