Yes, please do omit the quotes. As for guarding, I really don't think it'll be a problem to have a `zoom` that exists but is `undefined`, since we already do worse: https://github.com/jquery/jquery/blob/d55c46659b6008855e59541aede4d529b20f4337/src/support.js#L223.

But if you feel strongly about it, `!= null` seems best.