No way to insert NULLs using argument substitution (fix suggested)

There is no way to insert NULLs into a database using argument substitution (e.g. %d). This seems like a deficiency to me, and I have suggested a way to fix it. This is my first attempt at a core-improvement, and I would greatly appreciate comments about it.

Here the issue/patch:

http://drupal.org/node/186327

Thanks,

Nick