Blank line in select box

I have a taxonomy field that is set to appear as a select box. Beneath -None- there is a blank line before my first choice, like so:

-None-

100-200
200-400
400-700

How do I go about getting rid of it?

I've tried setting the field to required on both the taxonomy and cck sides with no luck. Worse yet, the " " line is read as a valid response if I make the field required, so a user could select it as a choice.