diff --git a/examples/public/middleware_use.php b/examples/public/middleware_use.php
index 32b17aff..f6a7fcf9 100644
--- a/examples/public/middleware_use.php
+++ b/examples/public/middleware_use.php
@@ -8,11 +8,11 @@
  */
 
 use League\OAuth2\Server\AuthorizationServer;
-use League\OAuth2\Server\ResourceServer;
 use League\OAuth2\Server\Grant\AuthCodeGrant;
 use League\OAuth2\Server\Grant\RefreshTokenGrant;
 use League\OAuth2\Server\Middleware\AuthorizationServerMiddleware;
 use League\OAuth2\Server\Middleware\ResourceServerMiddleware;
+use League\OAuth2\Server\ResourceServer;
 use OAuth2ServerExamples\Repositories\AccessTokenRepository;
 use OAuth2ServerExamples\Repositories\AuthCodeRepository;
 use OAuth2ServerExamples\Repositories\ClientRepository;
@@ -75,6 +75,7 @@ $app = new App([
             new AccessTokenRepository(),
             $publicKeyPath
         );
+
         return $server;
     },
 ]);
diff --git a/examples/public/refresh_token.php b/examples/public/refresh_token.php
index b4efd45b..25c32100 100644
--- a/examples/public/refresh_token.php
+++ b/examples/public/refresh_token.php
@@ -17,7 +17,6 @@ use OAuth2ServerExamples\Repositories\ScopeRepository;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Message\ServerRequestInterface;
 use Slim\App;
-use Zend\Diactoros\Stream;
 
 include __DIR__ . '/../vendor/autoload.php';
 
@@ -68,6 +67,7 @@ $app->post('/access_token', function (ServerRequestInterface $request, ResponseI
         return $exception->generateHttpResponse($response);
     } catch (\Exception $exception) {
         $response->getBody()->write($exception->getMessage());
+
         return $response->withStatus(500);
     }
 });
diff --git a/src/Grant/AuthCodeGrant.php b/src/Grant/AuthCodeGrant.php
index a8787a54..2a05355e 100644
--- a/src/Grant/AuthCodeGrant.php
+++ b/src/Grant/AuthCodeGrant.php
@@ -264,7 +264,7 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
                 throw OAuthServerException::invalidRequest('code_challenge');
             }
 
-            if (preg_match("/^[A-Za-z0-9-._~]{43,128}$/", $codeChallenge) !== 1) {
+            if (preg_match('/^[A-Za-z0-9-._~]{43,128}$/', $codeChallenge) !== 1) {
                 throw OAuthServerException::invalidRequest(
                     'code_challenge',
                     'The code_challenge must be between 43 and 128 characters'