diff --git a/src/DumpRecorder/MultiDumpHandler.php b/src/DumpRecorder/MultiDumpHandler.php
index dd341f3..93c08c6 100644
--- a/src/DumpRecorder/MultiDumpHandler.php
+++ b/src/DumpRecorder/MultiDumpHandler.php
@@ -14,7 +14,7 @@ public function dump($value)
         }
     }
 
-    public function addHandler(callable $callable = null): self
+    public function addHandler(?callable $callable = null): self
     {
         $this->handlers[] = $callable;
 
diff --git a/src/Payloads/CachePayload.php b/src/Payloads/CachePayload.php
index bcc92b3..c77adde 100644
--- a/src/Payloads/CachePayload.php
+++ b/src/Payloads/CachePayload.php
@@ -22,7 +22,7 @@ class CachePayload extends Payload
     /** @var int|null */
     protected $expirationInSeconds;
 
-    public function __construct(string $type, string $key, $tags, $value = null, int $expirationInSeconds = null)
+    public function __construct(string $type, string $key, $tags, $value = null, ?int $expirationInSeconds = null)
     {
         $this->type = $type;
 
diff --git a/src/Payloads/MailablePayload.php b/src/Payloads/MailablePayload.php
index 69b7623..bc548e4 100644
--- a/src/Payloads/MailablePayload.php
+++ b/src/Payloads/MailablePayload.php
@@ -19,7 +19,7 @@ public static function forMailable(Mailable $mailable)
         return new self(self::renderMailable($mailable), $mailable);
     }
 
-    public function __construct(string $html, Mailable $mailable = null)
+    public function __construct(string $html, ?Mailable $mailable = null)
     {
         $this->html = $html;
 
diff --git a/src/Ray.php b/src/Ray.php
index b1331e2..7f4ac17 100644
--- a/src/Ray.php
+++ b/src/Ray.php
@@ -44,7 +44,7 @@
 
 class Ray extends BaseRay
 {
-    public function __construct(Settings $settings, Client $client = null, string $uuid = null)
+    public function __construct(Settings $settings, ?Client $client = null, ?string $uuid = null)
     {
         // persist the enabled setting across multiple instantiations
         $enabled = static::$enabled;
@@ -487,7 +487,7 @@ public function stopShowingHttpClientRequests(): self
         return $this;
     }
 
-    protected function handleWatcherCallable(Watcher $watcher, Closure $callable = null)
+    protected function handleWatcherCallable(Watcher $watcher, ?Closure $callable = null)
     {
         $rayProxy = new RayProxy();