Jeff King authored Feb 26, 2016 and Junio C Hamano committed Feb 26, 2016

Sine the credential.helper key is a multi-valued config
list, there's no way to "unset" a helper once it's been set.
So if your system /etc/gitconfig sets one, you can never
avoid running it, but only add your own helpers on top.

Since an empty value for credential.helper is nonsensical
(it would just try to run "git-credential-"), we can assume
nobody is using it. Let's define it to reset the helper
list, letting you override lower-priority instances which
have come before.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>