In English, it's widely held that imperative verbs have "invisible" subjects, on the syntactic level. For example, we see look at yourself in the mirror, rather than *look at you in the mirror, which implies that there's some invisible "you"-like entity in the subject position, which just doesn't appear on the surface.
Is this a universal? Or are there languages in which imperatives have no syntactic subject at all?
(P.S. For some languages, there may be no way to know whether there's an "invisible" subject or not, since it wouldn't affect other words the way English pronouns can. I'm not as interested in these cases: I'm specifically curious if there are languages that would show evidence of an invisible subject, but don't. In other words, I'm looking for evidence of absence, not just absence of evidence.)