Your partner isn't going to pass 1NT when you have a 6-5 with a void in his suit. If he does, the opponents won't. If they do too, it might be the right spot. 1NT is more of a denial bid, making some noise without showing the values for a 2/1. It barely even suggests 1NT as a contract. If the alternatives in your mind are making some encouraging noise when you have a hopeless hand for partner, you better rethink that!