Fix PHP warnings: add strict_types and replace isset with explicit checks

Co-authored-by: egorsmkv <7875085+egorsmkv@users.noreply.github.com>

Author: Copilot

packages/default/notifier/index.php

@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use Symfony\Component\Notifier\Bridge\Telegram\TelegramOptions;
 use Symfony\Component\Notifier\Bridge\Telegram\TelegramTransportFactory;
 use Symfony\Component\Notifier\Chatter;
@@ -42,7 +44,7 @@ function main(array $args): array
 
     // Check required arguments
     foreach ($requiredArgs as $arg) {
-        if (!isset($args[$arg])) {
+        if (!array_key_exists($arg, $args) || $args[$arg] === null) {
             return wrap(['error' => sprintf('Please supply %s argument.', $arg)]);
         }
     }

packages/default/notifier/test.php

@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 error_reporting(E_ALL & ~E_DEPRECATED);
 
 require __DIR__ . '/vendor/autoload.php';

test.php

@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 require __DIR__ . '/packages/default/notifier/vendor/autoload.php';
 
 // Constants