Apply php-cs-fixer fix --rules nullable_type_declaration_for_default_null_value

Author: nicolas-grekas

Tests/ZulipTransportTest.php

@@ -25,7 +25,7 @@ final class ZulipTransportTest extends TransportTestCase
     /**
      * @return ZulipTransport
      */
-    public static function createTransport(HttpClientInterface $client = null): TransportInterface
+    public static function createTransport(?HttpClientInterface $client = null): TransportInterface
     {
         return (new ZulipTransport('testEmail', 'testToken', 'testChannel', $client ?? new MockHttpClient()))->setHost('test.host');
     }

ZulipOptions.php

@@ -24,7 +24,7 @@ final class ZulipOptions implements MessageOptionsInterface
     /** @var string|null */
     private $recipient;
 
-    public function __construct(string $topic = null, string $recipient = null)
+    public function __construct(?string $topic = null, ?string $recipient = null)
     {
         $this->topic = $topic;
         $this->recipient = $recipient;

ZulipTransport.php

@@ -31,7 +31,7 @@ final class ZulipTransport extends AbstractTransport
     private $token;
     private $channel;
 
-    public function __construct(string $email, string $token, string $channel, HttpClientInterface $client = null, EventDispatcherInterface $dispatcher = null)
+    public function __construct(string $email, string $token, string $channel, ?HttpClientInterface $client = null, ?EventDispatcherInterface $dispatcher = null)
     {
         $this->email = $email;
         $this->token = $token;