fix: Type void cannot be part of a union type declaration.

Author: SRWieZ

src/Dock.php

@@ -43,12 +43,14 @@ public function cancelBounce()
         $this->client->post('dock/cancel-bounce');
     }
 
-    public function badge(?string $label = null): void|string
+    public function badge(?string $label = null): ?string
     {
         if (is_null($label)) {
             return $this->client->get('dock/badge');
         }
 
         $this->client->post('dock/badge', ['label' => $label]);
+
+        return null;
     }
 }