Throw if mongodb/mongodb package is not available when configuring handlers

Author: jmikola

src/DependencyInjection/MonologExtension.php

@@ -267,6 +267,10 @@ private function buildHandler(ContainerBuilder $container, $name, array $handler
             case 'mongo':
                 trigger_deprecation('symfony/monolog-bundle', '3.11', 'The "mongo" handler type is deprecated in MonologBundle since version 3.11.0, use the "mongodb" type instead.');
 
+                if (!class_exists('MongoDB\Client')) {
+                    throw new \RuntimeException('The "mongo" handler requires the mongodb/mongodb package to be installed.');
+                }
+
                 if (isset($handler['mongo']['id'])) {
                     $client = new Reference($handler['mongo']['id']);
                 } else {
@@ -294,6 +298,10 @@ private function buildHandler(ContainerBuilder $container, $name, array $handler
                 break;
 
             case 'mongodb':
+                if (!class_exists('MongoDB\Client')) {
+                    throw new \RuntimeException('The "mongodb" handler requires the mongodb/mongodb package to be installed.');
+                }
+
                 if (isset($handler['mongodb']['id'])) {
                     $client = new Reference($handler['mongodb']['id']);
                 } else {