diff --git a/.github/workflows/phpstan.yml b/.github/workflows/phpstan.yml
new file mode 100644
index 0000000..de07f19
--- /dev/null
+++ b/.github/workflows/phpstan.yml
@@ -0,0 +1,26 @@
+name: PHPStan
+
+on: [push, pull_request]
+
+jobs:
+  phpstan:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@2.26.0
+        with:
+          php-version: '8.1'
+
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Install dependencies
+        run: |
+          composer install --no-interaction --no-progress --no-suggest
+
+      - name: Run PHPStan
+        run: |
+          composer analyse --error-format=github
diff --git a/composer.json b/composer.json
index 4d9b4b6..218bd24 100755
--- a/composer.json
+++ b/composer.json
@@ -25,7 +25,8 @@
     "cslant/telegram-git-notifier": "^1.3.1"
   },
   "require-dev": {
-    "friendsofphp/php-cs-fixer": "^v3.37.1"
+    "friendsofphp/php-cs-fixer": "^v3.37.1",
+    "phpstan/phpstan": "^1.10.39"
   },
   "autoload": {
     "psr-4": {
@@ -48,6 +49,7 @@
     "optimize-autoloader": true
   },
   "scripts": {
+    "analyse": "vendor/bin/phpstan",
     "format": "vendor/bin/php-cs-fixer fix --allow-risky=yes",
     "post-install-cmd": [
       "bash vendor/cslant/telegram-git-notifier/install.sh"
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
new file mode 100644
index 0000000..2e837cd
--- /dev/null
+++ b/phpstan.neon.dist
@@ -0,0 +1,6 @@
+parameters:
+    level: 8
+    paths:
+        - src
+    tmpDir: build/phpstan
+    checkMissingIterableValueType: false
diff --git a/src/Services/CallbackService.php b/src/Services/CallbackService.php
index 5182734..ae649fb 100644
--- a/src/Services/CallbackService.php
+++ b/src/Services/CallbackService.php
@@ -86,7 +86,13 @@ public function handle(): void
 
         $callback = str_replace(SettingConstant::SETTING_PREFIX, '', $callback);
 
-        if ($this->bot->setting->updateSetting($callback, !$this->bot->setting->getSettings()[$callback])) {
+        $settings = $this->bot->setting->getSettings();
+        if (array_key_exists($callback, $settings)
+            && $this->bot->setting->updateSetting(
+                $callback,
+                !$settings[$callback]
+            )
+        ) {
             $this->bot->editMessageReplyMarkup([
                 'reply_markup' => $this->bot->settingMarkup(),
             ]);