Please just leave it as is. The only misimpression I can think it might give as is is that it will be an "abstain" vote. Since that impression is quickly squashed by seeing the vote buttons stay and no reputation appear, it's not a problem.

Some of the suggestions (==, #) are just going to confuse people.

If anyone is that desirous to fix things, how about putting a link on the "Null vote" option in user settings to an explanation?