diff --git a/.gitignore b/.gitignore
index 40e6641..8605a57 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,3 +4,5 @@ phpunit.xml
 composer.lock
 .php_cs.cache
 .phpunit.result.cache
+.php-cs-fixer.cache
+
diff --git a/composer.json b/composer.json
index 4e9d4a4..6d88a14 100644
--- a/composer.json
+++ b/composer.json
@@ -29,7 +29,8 @@
     "require-dev": {
         "phpunit/phpunit": "~7.0|~8.0|~9.0",
         "phpstan/phpstan": "^0.12",
-        "phpstan/phpstan-phpunit": "^0.12"
+        "phpstan/phpstan-phpunit": "^0.12",
+        "friendsofphp/php-cs-fixer": "^3.41"
     },
     "suggest": {
         "splitbrain/php-archive": "Greatly reduces memory usage for the geoip2:update command"
diff --git a/src/Command/UpdateDatabaseCommand.php b/src/Command/UpdateDatabaseCommand.php
index af41481..e3ad51f 100644
--- a/src/Command/UpdateDatabaseCommand.php
+++ b/src/Command/UpdateDatabaseCommand.php
@@ -57,7 +57,7 @@ protected function configure(): void
                 $databases_help .= sprintf(' * <info>%s</info>'.PHP_EOL, $name);
             }
 
-            [$first, $second, ] = array_keys($this->databases);
+            [$first, $second] = array_keys($this->databases);
 
             $help .= <<<EOT
 
@@ -105,10 +105,10 @@ protected function execute(InputInterface $input, OutputInterface $output): int
                 throw new \InvalidArgumentException(sprintf('Undefined "%s" database.', $database));
             }
 
-            if (!array_key_exists('url', $this->databases[$database]) ||
-                !array_key_exists('path', $this->databases[$database]) ||
-                !is_string($this->databases[$database]['url']) ||
-                !is_string($this->databases[$database]['path'])
+            if (!array_key_exists('url', $this->databases[$database])
+                || !array_key_exists('path', $this->databases[$database])
+                || !is_string($this->databases[$database]['url'])
+                || !is_string($this->databases[$database]['path'])
             ) {
                 throw new \InvalidArgumentException(sprintf('Invalid "%s" database config.', $database));
             }
diff --git a/src/DependencyInjection/Configuration.php b/src/DependencyInjection/Configuration.php
index 36e145d..80cd13e 100644
--- a/src/DependencyInjection/Configuration.php
+++ b/src/DependencyInjection/Configuration.php
@@ -192,10 +192,10 @@ private function normalizeDefaultDatabase(NodeDefinition $root_node): void
             ->beforeNormalization()
             ->ifTrue(static function ($v): bool {
                 return
-                    is_array($v) &&
-                    !array_key_exists('default_database', $v) &&
-                    !empty($v['databases']) &&
-                    is_array($v['databases']);
+                    is_array($v)
+                    && !array_key_exists('default_database', $v)
+                    && !empty($v['databases'])
+                    && is_array($v['databases']);
             })
             ->then(static function (array $v): array {
                 $keys = array_keys($v['databases']);
@@ -268,10 +268,10 @@ private function validateAvailableDefaultDatabase(NodeDefinition $root_node): vo
             ->validate()
             ->ifTrue(static function ($v): bool {
                 return
-                    is_array($v) &&
-                    array_key_exists('default_database', $v) &&
-                    !empty($v['databases']) &&
-                    !array_key_exists($v['default_database'], $v['databases']);
+                    is_array($v)
+                    && array_key_exists('default_database', $v)
+                    && !empty($v['databases'])
+                    && !array_key_exists($v['default_database'], $v['databases']);
             })
             ->then(static function (array $v): array {
                 $databases = implode('", "', array_keys($v['databases']));
@@ -292,10 +292,10 @@ private function allowGlobalLicense(NodeDefinition $root_node): void
             ->beforeNormalization()
             ->ifTrue(static function ($v): bool {
                 return
-                    is_array($v) &&
-                    array_key_exists('license', $v) &&
-                    array_key_exists('databases', $v) &&
-                    is_array($v['databases']);
+                    is_array($v)
+                    && array_key_exists('license', $v)
+                    && array_key_exists('databases', $v)
+                    && is_array($v['databases']);
             })
             ->then(static function (array $v): array {
                 foreach ($v['databases'] as $name => $database) {
@@ -320,10 +320,10 @@ private function allowGlobalLocales(NodeDefinition $root_node): void
             ->beforeNormalization()
             ->ifTrue(static function ($v): bool {
                 return
-                    is_array($v) &&
-                    array_key_exists('locales', $v) &&
-                    array_key_exists('databases', $v) &&
-                    is_array($v['databases']);
+                    is_array($v)
+                    && array_key_exists('locales', $v)
+                    && array_key_exists('databases', $v)
+                    && is_array($v['databases']);
             })
             ->then(static function (array $v): array {
                 foreach ($v['databases'] as $name => $database) {
@@ -386,10 +386,10 @@ private function normalizeUrl(NodeDefinition $database_node): void
             ->beforeNormalization()
             ->ifTrue(static function ($v): bool {
                 return
-                    is_array($v) &&
-                    !array_key_exists('url', $v) &&
-                    array_key_exists('license', $v) &&
-                    array_key_exists('edition', $v);
+                    is_array($v)
+                    && !array_key_exists('url', $v)
+                    && array_key_exists('license', $v)
+                    && array_key_exists('edition', $v);
             })
             ->then(static function (array $v): array {
                 $v['url'] = sprintf(self::URL, urlencode($v['edition']), urlencode($v['license']));
diff --git a/src/Reader/ReaderFactory.php b/src/Reader/ReaderFactory.php
index 107d29c..067bdbc 100644
--- a/src/Reader/ReaderFactory.php
+++ b/src/Reader/ReaderFactory.php
@@ -41,7 +41,7 @@ public function __construct(array $databases, string $reader_class = Reader::cla
      *
      * @return Reader
      */
-    public function create(string $database, ?array $locales = null): Reader
+    public function create(string $database, array $locales = null): Reader
     {
         if (!array_key_exists($database, $this->databases)) {
             $databases = implode('", "', array_keys($this->databases));