diff --git a/tests/Models/NullEventAttributeTest.php b/tests/Models/NullEventAttributeTest.php
index 6d7652e..573e7b9 100644
--- a/tests/Models/NullEventAttributeTest.php
+++ b/tests/Models/NullEventAttributeTest.php
@@ -47,6 +47,6 @@ final class NullEventAttributeTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullEventAttribute(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullEventAttributeTypeTest.php b/tests/Models/NullEventAttributeTypeTest.php
index 979caff..b999662 100644
--- a/tests/Models/NullEventAttributeTypeTest.php
+++ b/tests/Models/NullEventAttributeTypeTest.php
@@ -47,6 +47,6 @@ final class NullEventAttributeTypeTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullEventAttributeType(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullEventAttributeValueTest.php b/tests/Models/NullEventAttributeValueTest.php
index 2a90266..3da7fff 100644
--- a/tests/Models/NullEventAttributeValueTest.php
+++ b/tests/Models/NullEventAttributeValueTest.php
@@ -47,6 +47,6 @@ final class NullEventAttributeValueTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullEventAttributeValue(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }