It could be that for some reason it's missing, and a first attempt to write to it just creates a regular file...
Date: Sat, 23 Jul 2016 04:38:42 +0700
From: Robert Elz <kre%munnari.OZ.AU@localhost>
Message-ID: <20406.1469223522%andromeda.noi.kre.to@localhost>
| That /dev/null turned into a regular file is another bug [...]
| (This turns out to be a bug in MAKEDEV [...]
Actually, not, it must be elsewhere, or as a result of something else.
kre