diff --git a/docs/03_mink_integration.md b/docs/03_mink_integration.md
index ac3a061..878f9ba 100644
--- a/docs/03_mink_integration.md
+++ b/docs/03_mink_integration.md
@@ -20,7 +20,6 @@ default:
     extensions:
         # ...
         Behat\MinkExtension:
-            base_url: 'http://example.com'
             sessions:
                 symfony:
                     symfony: ~
diff --git a/src/Driver/SymfonyDriver.php b/src/Driver/SymfonyDriver.php
index 6141925..fa3ae08 100644
--- a/src/Driver/SymfonyDriver.php
+++ b/src/Driver/SymfonyDriver.php
@@ -10,7 +10,7 @@ use Symfony\Component\HttpKernel\KernelInterface;
 
 final class SymfonyDriver extends BrowserKitDriver
 {
-    public function __construct(KernelInterface $kernel, string $baseUrl)
+    public function __construct(KernelInterface $kernel, ?string $baseUrl)
     {
         if (!$kernel->getContainer()->has('test.client')) {
             throw new \RuntimeException(sprintf(