diff --git a/tests/Models/NullPromotionAttributeTest.php b/tests/Models/NullPromotionAttributeTest.php
index eb19963..9598d1b 100644
--- a/tests/Models/NullPromotionAttributeTest.php
+++ b/tests/Models/NullPromotionAttributeTest.php
@@ -47,6 +47,6 @@ final class NullPromotionAttributeTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullPromotionAttribute(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullPromotionAttributeTypeTest.php b/tests/Models/NullPromotionAttributeTypeTest.php
index 534d8c0..126377b 100644
--- a/tests/Models/NullPromotionAttributeTypeTest.php
+++ b/tests/Models/NullPromotionAttributeTypeTest.php
@@ -47,6 +47,6 @@ final class NullPromotionAttributeTypeTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullPromotionAttributeType(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullPromotionAttributeValueTest.php b/tests/Models/NullPromotionAttributeValueTest.php
index 305a1bd..913af77 100644
--- a/tests/Models/NullPromotionAttributeValueTest.php
+++ b/tests/Models/NullPromotionAttributeValueTest.php
@@ -47,6 +47,6 @@ final class NullPromotionAttributeValueTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullPromotionAttributeValue(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullPromotionTest.php b/tests/Models/NullPromotionTest.php
index 2a1edeb..c64d96e 100644
--- a/tests/Models/NullPromotionTest.php
+++ b/tests/Models/NullPromotionTest.php
@@ -47,6 +47,6 @@ final class NullPromotionTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullPromotion(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }