Thomas Haller authored Aug 25, 2019 and Lubomir Rintel committed Sep 11, 2019

NetworkManager treats "gsm.apn" %NULL as setting an empty APN ("").
At least with ModemManager. With oFono, a %NULL APN means not to set
the "AccessPointName", so oFono implementation treats %NULL different
from "".

Soon the meaning will change to allow %NULL to automatically
obtain the APN from the mobile-broadband-provider-info. That will be a
change in behavior how to treat %NULL.

Anyway, since %NULL is accepted and in fact means to actually use "",
the empty word should be also accepted to explicitly choose this
behavior. This is especially important in combination with changing the
meaning of %NULL.