When opening Kali on WSL, a two-line error prints before the login prompt:

-bash: .: filename argument required
.: usage: . filename [arguments]

The error might repeat multiple times depending on the number of files /etc/profile.d. The problem is due to a for loop at the end of /etc/profile. I think the loop was supposed to use a variable, since you see it unset 'i' even though 'i' is never declared.

Original:
if [ -d /etc/profile.d ]; then
for i in /etc/profile.d/*.sh; do
if [ -r ]; then
.
fi
done
unset i
fi

Fixed:
if [ -d /etc/profile.d ]; then
for i in /etc/profile.d/*.sh; do
if [ -r $i ]; then
. $i
fi
done
unset i
fi