[Notifier] Transport possible to have null

Author: StaffNowa

Message/NullMessage.php

@@ -40,6 +40,6 @@ public function getOptions(): ?MessageOptionsInterface
 
     public function getTransport(): ?string
     {
-        return $this->decoratedMessage->getTransport() ?? 'null';
+        return $this->decoratedMessage->getTransport() ?? null;
     }
 }

Test/Constraint/NotificationTransportIsEqual.php

@@ -19,9 +19,9 @@
  */
 final class NotificationTransportIsEqual extends Constraint
 {
-    private string $expectedText;
+    private ?string $expectedText;
 
-    public function __construct(string $expectedText)
+    public function __construct(?string $expectedText)
     {
         $this->expectedText = $expectedText;
     }