There are a handful of night turns, rarely fully worked in summer unless stock has to be moved due to engineering work, although in winter when a frost is forecast the night person will be retained to run an 'ice train' if required.
With TfL's declared ambition to run weekend night services on LO you can expect night turns to increase in the new concession. As for whether the introduction of that goes smoothly in the light of what is happening on the underground presently, remains to be seen.