Weird lastlogin output

[Ottavio Caruso <ottavio2006-usenet2012%yahoo.com@localhost>]

Hi,

$ uname -a
NetBSD NetBSD 9.0_STABLE NetBSD 9.0_STABLE (GENERIC) #0: Sat May  9
08:21:36 UTC 2020
mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC
amd64

$ lastlogin
root  constty    Sun Aug 23 11:45:12 2020
(0)   constty    Sun Aug 23 11:47:49 2020
oc    constty    Mon Dec  7 10:55:59 2020

Any clue of what (0) could be?

-- 
Ottavio Caruso