[Q] Exit value

[~]$ procmail -f- /tmp/nofile < /dev/null
procmail: Couldn't read "/tmp/nofile"
[~]$ echo $?
0

Will someone please explain to me why procmail exits with a true value
when the specified rcfile doesn't exist?  It's clear procmail did not
process the input, so I'm not sure why procmail is returning success.

Thanks,
Sam