NetworkTransactionReference: id should not be required

src/Models/NetworkTransactionReference.php

@@ -19,7 +19,7 @@ use stdClass;
 class NetworkTransactionReference implements \JsonSerializable
 {
     /**
-     * @var string
+     * @var ?string
      */
     private $id;
 
@@ -39,9 +39,9 @@ class NetworkTransactionReference implements \JsonSerializable
     private $acquirerReferenceNumber;
 
     /**
-     * @param string $id
+     * @param string|null $id
      */
-    public function __construct(string $id)
+    public function __construct(?string $id = null)
     {
         $this->id = $id;
     }
@@ -53,7 +53,7 @@ class NetworkTransactionReference implements \JsonSerializable
      * is the "NRID" field in response. The pattern we expect for this field from Visa/Amex/CB/Discover is
      * numeric, Mastercard/BNPP is alphanumeric and Paysecure is alphanumeric with special character -.
      */
-    public function getId(): string
+    public function getId(): ?string
     {
         return $this->id;
     }
@@ -68,7 +68,7 @@ class NetworkTransactionReference implements \JsonSerializable
      * @required
      * @maps id
      */
-    public function setId(string $id): void
+    public function setId(?string $id): void
     {
         $this->id = $id;
     }
@@ -167,7 +167,9 @@ class NetworkTransactionReference implements \JsonSerializable
     public function jsonSerialize(bool $asArrayWhenEmpty = false)
     {
         $json = [];
-        $json['id']                            = $this->id;
+        if (isset($this->id)) {
+            $json['id']                        = $this->id;
+        }
         if (isset($this->date)) {
             $json['date']                      = $this->date;
         }