common: disable logging for level=NONE

Previously, we did not add any logging handlers when logger_level
was set to NONE. This made Monolog to default to a stderr handler.
Let’s use NullHandler to correctly disable logging.

NEWS.md

@@ -7,6 +7,7 @@
 ### Bug fixes
 - Reddit spout allows wider range of URLs, including absolute URLs and searches ([#1033](https://github.com/SSilence/selfoss/pull/1033))
 - Improved compatibility with PHP 7.2 ([#1049](https://github.com/SSilence/selfoss/issues/1049))
+- `logger_level=NONE` is now handled correctly ([#1077](https://github.com/SSilence/selfoss/issues/1077))
 
 ### API changes
 - `tags` attribute is now consistently array of strings, numbers are numbers and booleans are booleans. **This might break third-party clients that have not updated yet.** ([#948](https://github.com/SSilence/selfoss/pull/948))

common.php

@@ -2,6 +2,7 @@
 
 use Monolog\Formatter\LineFormatter;
 use Monolog\Handler\ErrorLogHandler;
+use Monolog\Handler\NullHandler;
 use Monolog\Handler\StreamHandler;
 use Monolog\Logger;
 
@@ -39,7 +40,9 @@
 
 // init logger
 $log = new Logger('selfoss');
-if ($f3->get('logger_level') !== 'NONE') {
+if ($f3->get('logger_level') === 'NONE') {
+    $log->pushHandler(new NullHandler);
+} else {
     $logger_destination = $f3->get('logger_destination');
 
     if (strpos($logger_destination, 'file:') === 0) {