diff --git a/phpstan-baseline.neon b/phpstan-baseline.neon
index 98d21c6..55548cf 100644
--- a/phpstan-baseline.neon
+++ b/phpstan-baseline.neon
@@ -900,6 +900,12 @@ parameters:
 			count: 1
 			path: src/Http/Middleware/ServerErrorHandler.php
 
+		-
+			message: '#^Binary operation "\." between non\-falsy\-string and array\<mixed\>\|string results in an error\.$#'
+			identifier: binaryOp.invalid
+			count: 1
+			path: src/Http/UriTemplate.php
+
 		-
 			message: '#^Method ShoppingFeed\\Sdk\\Http\\UriTemplate\:\:expand\(\) has no return type specified\.$#'
 			identifier: missingType.return
@@ -936,6 +942,12 @@ parameters:
 			count: 1
 			path: src/Http/UriTemplate.php
 
+		-
+			message: '#^Parameter \#2 \$array of function implode expects array\<string\>, array\<array\<mixed\>\|string\> given\.$#'
+			identifier: argument.type
+			count: 1
+			path: src/Http/UriTemplate.php
+
 		-
 			message: '#^Property ShoppingFeed\\Sdk\\Http\\UriTemplate\:\:\$delims type has no value type specified in iterable type array\.$#'
 			identifier: missingType.iterableValue
diff --git a/src/Client/Client.php b/src/Client/Client.php
index 36a121e..aacbee0 100644
--- a/src/Client/Client.php
+++ b/src/Client/Client.php
@@ -14,19 +14,14 @@ class Client
     private $client;
 
     /**
-     * @param ClientOptions|null  $options
-     *
      * @return \ShoppingFeed\Sdk\Api\Session\SessionResource
      */
-    public static function createSession(CredentialInterface $credential, ClientOptions $options = null)
+    public static function createSession(CredentialInterface $credential, ?ClientOptions $options = null)
     {
         return (new self($options))->authenticate($credential);
     }
 
-    /**
-     * @param ClientOptions|null $options
-     */
-    public function __construct(ClientOptions $options = null)
+    public function __construct(?ClientOptions $options = null)
     {
         if (null === $options) {
             $options = new ClientOptions();
diff --git a/src/Hal/HalLink.php b/src/Hal/HalLink.php
index 5d694bd..ae00553 100644
--- a/src/Hal/HalLink.php
+++ b/src/Hal/HalLink.php
@@ -199,8 +199,8 @@ public function delete($data, array $variables = [], array $options = [])
      */
     public function batchSend(
         $requests,
-        callable $success = null,
-        callable $error = null,
+        ?callable $success = null,
+        ?callable $error = null,
         array $options = [],
         $concurrency = 10,
     ) {
@@ -255,11 +255,9 @@ public function createRequest($method, array $variables = [], $body = null, $hea
     }
 
     /**
-     * @param callable|null $callback
-     *
      * @return \Closure
      */
-    private function createResponseCallback(callable $callback = null)
+    private function createResponseCallback(?callable $callback = null)
     {
         return function (ResponseInterface $response) use ($callback) {
             if ($callback) {
@@ -270,11 +268,9 @@ private function createResponseCallback(callable $callback = null)
     }
 
     /**
-     * @param callable|null $callback
-     *
      * @return \Closure
      */
-    private function createExceptionCallback(callable $callback = null)
+    private function createExceptionCallback(?callable $callback = null)
     {
         return function (Exception $exception) use ($callback) {
             call_user_func($callback, $exception);
diff --git a/src/Http/Adapter/GuzzleHTTPAdapter.php b/src/Http/Adapter/GuzzleHTTPAdapter.php
index ad09605..1dc0512 100644
--- a/src/Http/Adapter/GuzzleHTTPAdapter.php
+++ b/src/Http/Adapter/GuzzleHTTPAdapter.php
@@ -27,8 +27,8 @@ class GuzzleHTTPAdapter implements Http\Adapter\AdapterInterface
     private $pool;
 
     public function __construct(
-        Client\ClientOptions $options = null,
-        GuzzleHttp\HandlerStack $stack = null,
+        ?Client\ClientOptions $options = null,
+        ?GuzzleHttp\HandlerStack $stack = null,
     ) {
         $this->options = $options ?: new Client\ClientOptions();
         $this->stack   = $stack ?: $this->createHandlerStack();
@@ -106,11 +106,9 @@ public function withToken($token)
     }
 
     /**
-     * @param callable|null $callback
-     *
      * @return \Closure
      */
-    private function createExceptionCallback(callable $callback = null)
+    private function createExceptionCallback(?callable $callback = null)
     {
         return function (GuzzleHttp\Exception\TransferException $exception) use ($callback) {
             if ($callback && $exception instanceof GuzzleHttp\Exception\RequestException && $exception->hasResponse()) {
diff --git a/src/Http/Middleware/RateLimitHandler.php b/src/Http/Middleware/RateLimitHandler.php
index e305551..778df9a 100644
--- a/src/Http/Middleware/RateLimitHandler.php
+++ b/src/Http/Middleware/RateLimitHandler.php
@@ -23,22 +23,20 @@ class RateLimitHandler
     private $logger;
 
     /**
-     * @param int                  $maxRetries
-     * @param LoggerInterface|null $logger
+     * @param int $maxRetries
      */
-    public function __construct($maxRetries = 3, LoggerInterface $logger = null)
+    public function __construct($maxRetries = 3, ?LoggerInterface $logger = null)
     {
         $this->maxRetries = (int) $maxRetries;
         $this->logger     = $logger;
     }
 
     /**
-     * @param int                    $count
-     * @param ResponseInterface|null $response
+     * @param int $count
      *
      * @return bool
      */
-    public function decide($count, RequestInterface $request, ResponseInterface $response = null)
+    public function decide($count, RequestInterface $request, ?ResponseInterface $response = null)
     {
         if (! $response || $count >= $this->maxRetries) {
             return false;
diff --git a/src/Http/Middleware/ServerErrorHandler.php b/src/Http/Middleware/ServerErrorHandler.php
index 4f6fc5a..435af34 100644
--- a/src/Http/Middleware/ServerErrorHandler.php
+++ b/src/Http/Middleware/ServerErrorHandler.php
@@ -27,12 +27,11 @@ public function __construct($maxRetries = 3)
     }
 
     /**
-     * @param int                    $count
-     * @param ResponseInterface|null $response
+     * @param int $count
      *
      * @return bool
      */
-    public function decide($count, RequestInterface $request, ResponseInterface $response = null)
+    public function decide($count, RequestInterface $request, ?ResponseInterface $response = null)
     {
         if ($count >= $this->maxRetries) {
             return false;