Fixed null depecrations

Author: rolfdenhartog

src/Client.php

@@ -18,7 +18,7 @@ class Client
     public function __construct(
         string $host,
         string $apiKey,
-        HttpClient $httpClient = null
+        ?HttpClient $httpClient = null
     ) {
         $this->httpClient = $httpClient ?: HttpClientFactory::create($host, $apiKey);
         $this->messages = new MessagesService($this);

src/HttpClientFactory.php

@@ -9,7 +9,7 @@
 
 class HttpClientFactory
 {
-    public static function create(string $host, string $apiKey, callable $handler = null): Client
+    public static function create(string $host, string $apiKey, ?callable $handler = null): Client
     {
         if ($handler === null) {
             $handler = HandlerStack::create();

src/RetryMiddlewareFactory.php

@@ -25,8 +25,8 @@ public static function buildDecider(): callable
         return function (
             $retries,
             Request $request,
-            Response $response = null,
-            Throwable $exception = null
+            ?Response $response = null,
+            ?Throwable $exception = null
         ) {
             if ($retries > self::$maxRetries) {
                 return false;
@@ -48,18 +48,18 @@ public static function buildDelay(): callable
     {
         return function (
             $retries,
-            Response $response = null
+            ?Response $response = null
         ) {
             return self::$defaultRetryDelay;
         };
     }
 
-    private static function isConnectionError(\Throwable $exception = null): bool
+    private static function isConnectionError(?\Throwable $exception = null): bool
     {
         return $exception instanceof \GuzzleHttp\Exception\ConnectException;
     }
 
-    private static function isInternalServerError(\Throwable $exception = null): bool
+    private static function isInternalServerError(?\Throwable $exception = null): bool
     {
         return $exception instanceof \GuzzleHttp\Exception\ServerException;
     }