NULL as default type

[muntzen]

Howdy! I'm loving this library, it's really saving me a ton of time.
However, I'd much rather NULL be the default type for values added to
the database, particularly for dates - I had a DATE field that was
causing problems because sqlite wouldn't convert '' to a date happily
from the app (it would from the command-line, good times). Anyhows, I
spent the day yesterday learning how everything worked (I'm kinda new
to JavaScript) and changing the library to default values to null. It
seems to be working well for all my use cases. Is this something
people would be interested in me committing back to the repo? I'd be
glad to post my altered code and a diff if that'd be useful. I'm
using this in an AIR project, so my change was to "active.air.js".

And, errr, if there was some wicked easy way to take care of this that
I totally missed, please let me know. :)

Thanks!
-Eric