Before this commit empty Monolog loggers (or at least when no handlers are
defined) were assigned (by Monolog 1.x) the stream handler php://stderr with
the level 'debug'. This whole behaviour from MediaWiki config to Monolog is
unexpected; in the outcomes, depending on the PHP execution program, stderr
is or is not saved somewhere by default, leading to very different behaviours.
The behaviour will change in Monolog 2.x and nothing will happen is such cases
(similar hence to a NullHandler). With this commit the behaviour is uniform
accross all environments and (future) Monolog version: nothing is logged if
no handler is defined.
Precisely, a NullHandler for a given logger/MediaWiki logging channel is
defined here either when there is no key 'handlers', either when this key is
an empty array or 'false'.
Bug: T196906
Change-Id: I124391cc7b4485081980c5015431404234f40073
069c81bfe5