diff --git a/.github/workflows/code-style.yml b/.github/workflows/code-style.yml
new file mode 100644
index 0000000..9e8dd7c
--- /dev/null
+++ b/.github/workflows/code-style.yml
@@ -0,0 +1,42 @@
+name: PHP-CS-Fixer
+
+on:
+    push:
+        branches: [ master, main ]
+    pull_request:
+        branches: [ master, main ]
+
+permissions:
+    contents: read
+
+jobs:
+    code-style:
+
+        runs-on: ubuntu-latest
+        permissions:
+            contents: write  # for Git to git apply
+
+        steps:
+            -   uses: actions/checkout@v3
+
+            -   name: Setup PHP
+                uses: shivammathur/setup-php@v2
+                with:
+                    php-version: '8.3'
+                    extensions: gd, intl, pdo_mysql
+                    coverage: none # disable xdebug, pcov
+
+            # install dependencies from composer.json
+            -   name: Install test dependencies
+                env:
+                    COMPOSER: composer.json
+                run: composer install --prefer-dist --no-progress
+
+            # run php-cs-fixer, fix code styles
+            -   name: Run PHP CS Fixer
+                run: composer cs-fix
+
+            # commit and push fixed files
+            -   uses: stefanzweifel/git-auto-commit-action@v4
+                with:
+                    commit_message: Apply php-cs-fixer changes
diff --git a/.gitignore b/.gitignore
index ea75c5d..72c620d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,3 +7,7 @@ fragments/.DS_Store
 /playwright-report/
 /playwright/.cache/
 /screens/
+/.idea
+/composer.lock
+/.php-cs-fixer.cache
+/vendor
diff --git a/.php-cs-fixer.dist.php b/.php-cs-fixer.dist.php
new file mode 100644
index 0000000..72be593
--- /dev/null
+++ b/.php-cs-fixer.dist.php
@@ -0,0 +1,11 @@
+<?php
+
+declare(strict_types=1);
+
+$finder = (new PhpCsFixer\Finder())
+    ->in(__DIR__)
+;
+
+return (new Redaxo\PhpCsFixerConfig\Config())
+    ->setFinder($finder)
+    ;
diff --git a/boot.php b/boot.php
index 4c325b3..677bdeb 100644
--- a/boot.php
+++ b/boot.php
@@ -1,5 +1,7 @@
 <?php
 
+use FriendsOfREDAXO\Maintenance\Maintenance;
+
 /**
  * This file is part of the maintenance package.
  *
@@ -13,19 +15,18 @@
 if (rex::isSetup()) {
     return;
 }
-rex_extension::register('PACKAGES_INCLUDED', function () {
+rex_extension::register('PACKAGES_INCLUDED', static function () {
     $addon = rex_addon::get('maintenance');
 
-    if (rex::isFrontend() && boolval($addon->getConfig('block_frontend'))) {
-
-        \FriendsOfREDAXO\Maintenance\Maintenance::checkFrontend();
+    if (rex::isFrontend() && (bool) $addon->getConfig('block_frontend')) {
+        Maintenance::checkFrontend();
     }
-    if (rex::isBackend() && boolval($addon->getConfig('block_backend'))) {
-        \FriendsOfREDAXO\Maintenance\Maintenance::checkBackend();
+    if (rex::isBackend() && (bool) $addon->getConfig('block_backend')) {
+        Maintenance::checkBackend();
     }
 
     if (rex::isBackend()) {
-        \FriendsOfREDAXO\Maintenance\Maintenance::setIndicators();
+        Maintenance::setIndicators();
         rex_view::addJsFile($addon->getAssetsUrl('dist/bootstrap-tokenfield.js'));
         rex_view::addJsFile($addon->getAssetsUrl('dist/init_bootstrap-tokenfield.js'));
         rex_view::addCssFile($addon->getAssetsUrl('dist/css/bootstrap-tokenfield.css'));
@@ -35,7 +36,7 @@
         if ('maintenance/frontend' === rex_be_controller::getCurrentPage()) {
             rex_extension::register('OUTPUT_FILTER', static function (rex_extension_point $ep) {
                 $suchmuster = 'class="###maintenance-settings-editor###"';
-                $ersetzen = strval(rex_config::get('maintenance', 'editor')); // @phpstan-ignore-line
+                $ersetzen = (string) rex_config::get('maintenance', 'editor'); // @phpstan-ignore-line
                 $ep->setSubject(str_replace($suchmuster, $ersetzen, $ep->getSubject())); // @phpstan-ignore-line
             });
         }
diff --git a/composer.json b/composer.json
new file mode 100644
index 0000000..e8dda5e
--- /dev/null
+++ b/composer.json
@@ -0,0 +1,14 @@
+{
+  "require-dev": {
+    "redaxo/php-cs-fixer-config": "^2.0",
+    "friendsofphp/php-cs-fixer": "^3.14"
+  },
+  "replace": {
+    "psr/log": "*",
+    "psr/container": "*"
+  },
+  "scripts": {
+    "cs-dry": "php-cs-fixer fix -v --ansi --dry-run --config=.php-cs-fixer.dist.php",
+    "cs-fix": "php-cs-fixer fix -v --ansi --config=.php-cs-fixer.dist.php"
+  }
+}
diff --git a/fragments/maintenance/announcement.php b/fragments/maintenance/announcement.php
index 54009ce..5901468 100644
--- a/fragments/maintenance/announcement.php
+++ b/fragments/maintenance/announcement.php
@@ -4,10 +4,10 @@
 $end_date = rex_config::get('maintenance', 'announcement_end_date');
 $current_date = date('Y-m-d\TH:i:s');
 
-if ($announcement !== '' && $start_date <= $current_date && $end_date >= $current_date) {
+if ('' !== $announcement && $start_date <= $current_date && $end_date >= $current_date) {
     ?>
 <div class="maintenance-announcement">
-    <?php echo $announcement; ?>
+    <?= $announcement ?>
 </div>
 <?php }
 ?>
diff --git a/fragments/maintenance/login.php b/fragments/maintenance/login.php
index bc0a3d1..91b651a 100644
--- a/fragments/maintenance/login.php
+++ b/fragments/maintenance/login.php
@@ -1,7 +1,7 @@
 <?php
-if(rex_config::get('maintenance', 'authentification_mode', '') === 'password') { ?>
+if ('password' === rex_config::get('maintenance', 'authentification_mode', '')) { ?>
 <div class="maintenance-login">
-    <form action="<?= rex_url::base(); ?>" method="post">
+    <form action="<?= rex_url::base() ?>" method="post">
     <label for="maintenance_secret">Access-Code</label>
     <input name="maintenance_secret" class="maintenance-pw-input" type="password" placeholder=""/>
     <button type="submit" class="maintenance-pw-btn">Login</button>
diff --git a/fragments/maintenance/reload.php b/fragments/maintenance/reload.php
index 30ae048..b63ccb8 100644
--- a/fragments/maintenance/reload.php
+++ b/fragments/maintenance/reload.php
@@ -2,5 +2,5 @@
 // reload current frontend page html button
 ?>
 <div class="maintenance-reload">
-    <a href="<?= $_SERVER['REQUEST_URI']; ?>" class="maintenance-btn">Reload</a>
+    <a href="<?= $_SERVER['REQUEST_URI'] ?>" class="maintenance-btn">Reload</a>
 </div>
diff --git a/install.php b/install.php
index ab27c6e..6aad2f9 100644
--- a/install.php
+++ b/install.php
@@ -12,7 +12,7 @@
 $addon = rex_addon::get('maintenance');
 
 /**
- * Addon in Setup-Addons mit aufnehmen der config.yml in dieser Installation aufnehmen
+ * Addon in Setup-Addons mit aufnehmen der config.yml in dieser Installation aufnehmen.
  */
 $config_file = rex_path::coreData('config.yml');
 $data = rex_file::getConfig($config_file);
@@ -22,7 +22,7 @@
 }
 
 /* Eigene IP-Adresse in die erlaubten IP-Adressen hinzufügen, sofern nicht bereits vorhanden */
-$allowed_ips = strval($addon->getConfig('allowed_ips')); // @phpstan-ignore-line
+$allowed_ips = (string) $addon->getConfig('allowed_ips'); /** @phpstan-ignore-line */
 $allowed_ips = array_filter(explode(',', $allowed_ips)); // Leere Elemente entfernen
 $ip = rex_server('SERVER_ADDR', 'string', '');
 
@@ -34,10 +34,10 @@
 }
 
 /* Bei Installation standardmäßig ein zufälliges Secret generieren */
-if ($addon->getConfig('maintenance_secret') === '') {
+if ('' === $addon->getConfig('maintenance_secret')) {
     $addon->setConfig('maintenance_secret', bin2hex(random_bytes(16)));
 }
 
-if($addon->getConfig('announcement') === '') {
+if ('' === $addon->getConfig('announcement')) {
     $addon->setConfig('announcement', '<p>Geplante Wartungsarbeiten am 01.01.2022 von 00:00 bis 06:00 Uhr. In dieser Zeit ist die Website möglicherweise nicht erreichbar.</p>');
 }
diff --git a/lib/Maintenance.php b/lib/Maintenance.php
index e660cce..368264e 100644
--- a/lib/Maintenance.php
+++ b/lib/Maintenance.php
@@ -15,27 +15,28 @@
 use rex;
 use rex_addon;
 use rex_article;
-use rex_clang;
-use rex_response;
-use rex_yrewrite;
-use rex_session;
-use rex_request;
-use rex_unset_session;
 use rex_backend_login;
-use rex_user;
-use rex_login;
-use rex_server;
+use rex_clang;
 use rex_extension;
 use rex_extension_point;
 use rex_fragment;
+use rex_login;
+use rex_response;
+use rex_user;
+use rex_yrewrite;
+
+use function in_array;
+
+use const FILTER_VALIDATE_IP;
+use const FILTER_VALIDATE_URL;
 
 class Maintenance
 {
     /** @api */
     public function checkUrl(string $url): ?bool
     {
-        if ($url !== '') {
-            if (filter_var($url, FILTER_VALIDATE_URL) === false) {
+        if ('' !== $url) {
+            if (false === filter_var($url, FILTER_VALIDATE_URL)) {
                 return false;
             }
             return true;
@@ -46,11 +47,10 @@ public function checkUrl(string $url): ?bool
     /** @api */
     public function checkIp(string $ip): ?bool
     {
-        if ($ip !== '' && filter_var($ip, FILTER_VALIDATE_IP) === false) {
+        if ('' !== $ip && false === filter_var($ip, FILTER_VALIDATE_IP)) {
             return false;
-        } else {
-            return true;
         }
+        return true;
     }
 
     /** @api */
@@ -58,9 +58,9 @@ public static function isIpAllowed(): bool
     {
         $addon = rex_addon::get('maintenance');
         $ip = rex_server('REMOTE_ADDR', 'string', '');
-        $allowedIps = strval($addon->getConfig('allowed_ips')); // @phpstan-ignore-line
+        $allowedIps = (string) $addon->getConfig('allowed_ips'); // @phpstan-ignore-line
 
-        if ($allowedIps !== '') {
+        if ('' !== $allowedIps) {
             $allowedIpsArray = explode(',', $allowedIps);
             return in_array($ip, $allowedIpsArray, true);
         }
@@ -73,9 +73,9 @@ public static function isHostAllowed(): bool
     {
         $addon = rex_addon::get('maintenance');
         $host = rex_server('HTTP_HOST', 'string', '');
-        $allowedHosts = strval($addon->getConfig('allowed_yrewrite_domains', false)); // @phpstan-ignore-line
+        $allowedHosts = (string) $addon->getConfig('allowed_yrewrite_domains', false); // @phpstan-ignore-line
 
-        if ($allowedHosts !== '') {
+        if ('' !== $allowedHosts) {
             $allowedHostsArray = explode(',', $allowedHosts);
             return in_array($host, $allowedHostsArray, true);
         }
@@ -89,9 +89,9 @@ public static function isYrewriteDomainAllowed(): bool
         $addon = rex_addon::get('maintenance');
         if ($ydomain = rex_yrewrite::getDomainByArticleId(rex_article::getCurrentId(), rex_clang::getCurrentId())) {
             $yrewrite_domain = $ydomain->getHost();
-            $allowedDomains = strval($addon->getConfig('allowed_yrewrite_domains')); // @phpstan-ignore-line
+            $allowedDomains = (string) $addon->getConfig('allowed_yrewrite_domains'); // @phpstan-ignore-line
 
-            if ($allowedDomains !== '') {
+            if ('' !== $allowedDomains) {
                 $allowedDomainsArray = explode('|', $allowedDomains);
                 return in_array($yrewrite_domain, $allowedDomainsArray, true);
             }
@@ -104,17 +104,17 @@ public static function isYrewriteDomainAllowed(): bool
     public static function isSecretAllowed(): bool
     {
         $addon = rex_addon::get('maintenance');
-        $config_secret = strval($addon->getConfig('maintenance_secret'));
+        $config_secret = (string) $addon->getConfig('maintenance_secret');
 
         // Bereits mit richtigem Secret eingeloggt
-        if ($config_secret != '' && rex_session('maintenance_secret', 'string', '') === $config_secret) { // @phpstan-ignore-line
+        if ('' != $config_secret && rex_session('maintenance_secret', 'string', '') === $config_secret) { // @phpstan-ignore-line
             return true;
         }
 
         $maintenance_secret = rex_request('maintenance_secret', 'string', '');
         $authentification_mode = $addon->getConfig('authentification_mode');
 
-        if (($authentification_mode === 'URL' || $authentification_mode === 'password') && $config_secret != '' && $maintenance_secret === $config_secret) {
+        if (('URL' === $authentification_mode || 'password' === $authentification_mode) && '' != $config_secret && $maintenance_secret === $config_secret) {
             rex_set_session('maintenance_secret', $maintenance_secret);
             return true;
         }
@@ -136,7 +136,7 @@ public static function isUserAllowed(): bool
         }
 
         // Eingeloggte REDAXO-Benutzer dürfen sich einloggen, wenn es in den Einstellungen erlaubt ist
-        if ($user instanceof rex_user && boolval($addon->getConfig('allow_logged_in_users'))) {
+        if ($user instanceof rex_user && (bool) $addon->getConfig('allow_logged_in_users')) {
             return true;
         }
 
@@ -178,7 +178,7 @@ public static function checkFrontend(): void
 
         // Wenn die Sitemap angefordert wird, Anfrage nicht sperren
         $REQUEST_URI = rex_server('REQUEST_URI', 'string', '');
-        if (str_contains($REQUEST_URI, 'sitemap.xml') === true) {
+        if (true === str_contains($REQUEST_URI, 'sitemap.xml')) {
             return;
         }
 
@@ -192,11 +192,11 @@ public static function checkFrontend(): void
         }
 
         // Alles, was bis hier hin nicht erlaubt wurde, blockieren wie in den Einstellungen gewählt
-        $redirect_url = strval($addon->getConfig('redirect_frontend_to_url')); // @phpstan-ignore-line
-        $responsecode = strval($addon->getConfig('http_response_code')); // @phpstan-ignore-line
+        $redirect_url = (string) $addon->getConfig('redirect_frontend_to_url'); /** @phpstan-ignore-line */
+        $responsecode = (string) $addon->getConfig('http_response_code'); /** @phpstan-ignore-line */
 
         $mpage = new rex_fragment();
-        if ($redirect_url !== '') {
+        if ('' !== $redirect_url) {
             rex_response::setStatus(rex_response::HTTP_MOVED_TEMPORARILY);
             rex_response::sendRedirect($redirect_url);
         }
@@ -209,11 +209,11 @@ public static function checkBackend(): void
         $addon = rex_addon::get('maintenance');
 
         if (rex::getUser() instanceof rex_user && !rex::getUser()->isAdmin() && !rex::getImpersonator()) {
-            if (strval($addon->getConfig('redirect_backend_to_url'))) { // @phpstan-ignore-line
-                rex_response::sendRedirect(strval($addon->getConfig('redirect_backend_to_url')));  // @phpstan-ignore-line
+            if ((string) $addon->getConfig('redirect_backend_to_url')) { // @phpstan-ignore-line
+                rex_response::sendRedirect((string) $addon->getConfig('redirect_backend_to_url'));  // @phpstan-ignore-line
             }
             $mpage = new rex_fragment();
-            header('HTTP/1.1 ' . strval($addon->getConfig('http_response_code'))); // @phpstan-ignore-line
+            header('HTTP/1.1 ' . (string) $addon->getConfig('http_response_code')); // @phpstan-ignore-line
             exit($mpage->parse('maintenance/backend.php'));
         }
     }
@@ -223,13 +223,13 @@ public static function setIndicators(): void
         $addon = rex_addon::get('maintenance');
         $page = $addon->getProperty('page');
 
-        if (boolval($addon->getConfig('block_backend'))) {
+        if ((bool) $addon->getConfig('block_backend')) {
             $page['title'] .= ' <span class="label label-info pull-right">B</span>';
             $page['icon'] .= ' fa-toggle-on block_backend';
             $addon->setProperty('page', $page);
         }
 
-        if (boolval($addon->getConfig('block_frontend'))) {
+        if ((bool) $addon->getConfig('block_frontend')) {
             $page['title'] .= ' <span class="label label-danger pull-right">F</span>';
             $page['icon'] .= ' fa-toggle-on block_frontend';
         }
@@ -248,12 +248,12 @@ public static function getAnnouncement(): string
     {
         $addon = rex_addon::get('maintenance');
 
-        if (strval($addon->getConfig('announcement_start_date')) !== '') {  // @phpstan-ignore-line
-            $start = strtotime(strval($addon->getConfig('announcement_start_date'))); // @phpstan-ignore-line
-            $end = strtotime(strval($addon->getConfig('announcement_end_date'))); // @phpstan-ignore-line
+        if ('' !== (string) $addon->getConfig('announcement_start_date')) {  /** @phpstan-ignore-line */
+            $start = strtotime((string) $addon->getConfig('announcement_start_date')); /** @phpstan-ignore-line */
+            $end = strtotime((string) $addon->getConfig('announcement_end_date')); /** @phpstan-ignore-line */
             $now = time();
             if ($now >= $start && $now <= $end) {
-                return strval($addon->getConfig('announcement')); // @phpstan-ignore-line
+                return (string) $addon->getConfig('announcement'); // @phpstan-ignore-line
             }
         }
 
diff --git a/lib/command/maintenance_off.php b/lib/command/maintenance_off.php
index c72f4fe..e459fae 100644
--- a/lib/command/maintenance_off.php
+++ b/lib/command/maintenance_off.php
@@ -1,4 +1,5 @@
 <?php
+
 use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Output\OutputInterface;
 
diff --git a/lib/command/maintenance_on.php b/lib/command/maintenance_on.php
index 6bee755..bef0c0b 100644
--- a/lib/command/maintenance_on.php
+++ b/lib/command/maintenance_on.php
@@ -1,4 +1,5 @@
 <?php
+
 use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Output\OutputInterface;
 
diff --git a/pages/backend.php b/pages/backend.php
index abe35ed..611bf30 100644
--- a/pages/backend.php
+++ b/pages/backend.php
@@ -10,8 +10,6 @@
  * file that was distributed with this source code.
  */
 
-use FriendsOfREDAXO\Maintenance\MaintenanceUtil;
-
 $addon = rex_addon::get('maintenance');
 
 $form = rex_config_form::factory($addon->getName());
diff --git a/pages/frontend.php b/pages/frontend.php
index ea6af34..bb256f5 100644
--- a/pages/frontend.php
+++ b/pages/frontend.php
@@ -10,8 +10,6 @@
  * file that was distributed with this source code.
  */
 
-use FriendsOfREDAXO\Maintenance\MaintenanceUtil;
-
 $addon = rex_addon::get('maintenance');
 
 $form = rex_config_form::factory($addon->getName());
@@ -65,14 +63,13 @@
 // Erlaubte IP-Adressen
 $field = $form->addTextField('allowed_ips');
 $field->setLabel($addon->i18n('maintenance_allowed_ips_label'));
-$field->setNotice($addon->i18n('maintenance_allowed_ips_notice', \rex_server('REMOTE_ADDR', 'string', ''), \rex_server('SERVER_ADDR', 'string', '')));
+$field->setNotice($addon->i18n('maintenance_allowed_ips_notice', rex_server('REMOTE_ADDR', 'string', ''), rex_server('SERVER_ADDR', 'string', '')));
 $field->setAttribute('class', 'form-control');
 $field->setAttribute('data-maintenance', 'tokenfield');
 $field->setAttribute('data-beautify', 'false');
 
-
 // Wenn YRewrite installiert, dann erlaubte YRewrite-Domains auswählen
-if (\rex_addon::get('yrewrite')->isAvailable() && count(\rex_yrewrite::getDomains()) > 1) {
+if (rex_addon::get('yrewrite')->isAvailable() && count(rex_yrewrite::getDomains()) > 1) {
     $field = $form->addSelectField('allowed_yrewrite_domains');
     $field->setAttribute('multiple', 'multiple');
 
@@ -81,7 +78,7 @@
     $field->setLabel($addon->i18n('maintenance_allowed_yrewrite_domains_label'));
     $field->setNotice($addon->i18n('maintenance_allowed_yrewrite_domains_notice'));
     $select = $field->getSelect();
-    foreach (\rex_yrewrite::getDomains() as $key => $domain) {
+    foreach (rex_yrewrite::getDomains() as $key => $domain) {
         $select->addOption($key, $key);
     }
 }
@@ -101,7 +98,7 @@
 $field = $form->addTextAreaField('announcement');
 $field->setLabel($addon->i18n('maintenance_announcement_label'));
 $field->setNotice($addon->i18n('maintenance_announcement_notice'));
-if (strval(rex_config::get('maintenance', 'editor')) !== '') { // @phpstan-ignore-line
+if ('' !== (string) rex_config::get('maintenance', 'editor')) { // @phpstan-ignore-line
     $field->setAttribute('class', '###maintenance-settings-editor###');
 }
 
@@ -121,7 +118,6 @@
 $field->setNotice($addon->i18n('maintenance_announcement_end_date_notice', date('Y-m-d H:i:s')));
 $field->setAttribute('type', 'datetime-local');
 
-
 $fragment = new rex_fragment();
 $fragment->setVar('class', 'edit');
 $fragment->setVar('title', $addon->i18n('maintenance_settings_frontend_title'));
@@ -158,16 +154,16 @@
 
 // Ebenfalls für alle YRewrite-Domains ausgeben
 
-if (\rex_addon::get('yrewrite')->isAvailable() && count(\rex_yrewrite::getDomains()) > 1) {
-    foreach (\rex_yrewrite::getDomains() as $key => $domain) {
-        if($key == 'default') {
+if (rex_addon::get('yrewrite')->isAvailable() && count(rex_yrewrite::getDomains()) > 1) {
+    foreach (rex_yrewrite::getDomains() as $key => $domain) {
+        if ('default' == $key) {
             continue;
         }
         $url = $domain->getUrl() . '?maintenance_secret=' . rex_config::get('maintenance', 'maintenance_secret');
-        $copy .= '<li class="list-group-item"><label for="maintenance-mode-url-'.$key.'">YRewrite '. $key . '</label>';
+        $copy .= '<li class="list-group-item"><label for="maintenance-mode-url-' . $key . '">YRewrite ' . $key . '</label>';
         $copy .= '<div class="hidden" id="maintenance-mode-url-' . $key . '"><code>' . $url . '</code></div>';
         $copy .= '
-        <clipboard-copy for="maintenance-mode-url-'.$key.'" class="input-group">
+        <clipboard-copy for="maintenance-mode-url-' . $key . '" class="input-group">
           <input type="text" value="' . $url . '" readonly class="form-control">
           <span class="input-group-addon"><i class="rex-icon fa-clone"></i></span>
         </clipboad-copy></li>';
diff --git a/pages/index.php b/pages/index.php
index 5063d81..7cbc95b 100644
--- a/pages/index.php
+++ b/pages/index.php
@@ -11,5 +11,5 @@
 $addon = rex_addon::get('maintenance');
 echo rex_view::title($addon->i18n('title'));
 
-//include rex_be_controller::getCurrentPageObject()->getSubPath();
+// include rex_be_controller::getCurrentPageObject()->getSubPath();
 rex_be_controller::includeCurrentPageSubPath();
diff --git a/uninstall.php b/uninstall.php
index 8d89c18..6d6a5c3 100644
--- a/uninstall.php
+++ b/uninstall.php
@@ -3,8 +3,8 @@
 /* Bei Deinstallation des Addons aus der config.yml entfernen */
 $config_file = rex_path::coreData('config.yml');
 $data = rex_file::getConfig($config_file);
-if (key_exists('setup_addons', $data) && in_array('maintenance', $data['setup_addons'], true)) {
-    $data['setup_addons'] = array_filter($data['setup_addons'], fn ($e) => $e !== 'maintenance');
+if (array_key_exists('setup_addons', $data) && in_array('maintenance', $data['setup_addons'], true)) {
+    $data['setup_addons'] = array_filter($data['setup_addons'], static fn ($e) => 'maintenance' !== $e);
     rex_file::putConfig($config_file, $data);
 }
 
diff --git a/update.php b/update.php
index 64515ce..d6a432f 100644
--- a/update.php
+++ b/update.php
@@ -1,4 +1,5 @@
 <?php
+
 $addon = rex_addon::get('maintenance');
 
 // Upgrade from 2.x to 3.x
@@ -12,7 +13,7 @@
     }
 
     if ($addon->hasConfig('frontend_aktiv')) {
-        $addon->setConfig('block_frontend', $addon->getConfig('frontend_aktiv') === 'Deaktivieren' ? 0 : 1);
+        $addon->setConfig('block_frontend', 'Deaktivieren' === $addon->getConfig('frontend_aktiv') ? 0 : 1);
     }
 
     if ($addon->hasConfig('redirect_frontend')) {
@@ -24,15 +25,15 @@
     }
 
     if ($addon->hasConfig('backend_aktiv')) {
-        $addon->setConfig('block_backend', $addon->getConfig('backend_aktiv') === '1' ? 1 : 0);
+        $addon->setConfig('block_backend', '1' === $addon->getConfig('backend_aktiv') ? 1 : 0);
     }
 
     if ($addon->hasConfig('blockSession')) {
-        $addon->setConfig('block_frontend_rex_user', $addon->getConfig('blockSession') === 'Inaktiv' ? 0 : 1);
+        $addon->setConfig('block_frontend_rex_user', 'Inaktiv' === $addon->getConfig('blockSession') ? 0 : 1);
     }
 
     if ($addon->hasConfig('type')) {
-        $addon->setConfig('authentification_mode', $addon->getConfig('type') === 'Password' ? 'password' : 'URL');
+        $addon->setConfig('authentification_mode', 'Password' === $addon->getConfig('type') ? 'password' : 'URL');
     }
 
     if ($addon->hasConfig('secret')) {