Update Notification.php

Line 67 had an invalid '?' at "?string $image_url = null.

Removed the '?'

    public function __construct(string $title = '', string $body = '', string $recipient = '', string $sound = '', string $icon = '', string $color = '', int $badge = 0, string $tag = '', string $subtitle = '', array $data = [], string $click_action = '', ?string $image_url = null)

src/Push/Notification.php

@@ -64,7 +64,7 @@ class Notification implements Request
      * @param string $body
      * @param string $recipient
      */
-    public function __construct(string $title = '', string $body = '', string $recipient = '', string $sound = '', string $icon = '', string $color = '', int $badge = 0, string $tag = '', string $subtitle = '', array $data = [], string $click_action = '', ?string $image_url = null)
+    public function __construct(string $title = '', string $body = '', string $recipient = '', string $sound = '', string $icon = '', string $color = '', int $badge = 0, string $tag = '', string $subtitle = '', array $data = [], string $click_action = '', string $image_url = null)
     {
         $this->title = $title;
         $this->body = $body;