Sending Email to Undisclosed Recipient List with GMail

I've always wondered how one sends email to multiple recipients in Gmail while keeping the "To:" address list as "undisclosed". I would normally put some generic email address on the "To:" box (ex. myself, or some info@xxxxx address) just to keep it filled, then put the real recipients on the "Bcc:" list so that they do not appear to each other.

As it turns out, the "To:" address in GMail is optional. It does not really have to be filled-in. So to send to a list of undisclosed recipients, just put all the addresses on the "Bcc:" box and keep the "To:" box empty! It works and does not prompt an error about having an empty "To:" box.