diff --git a/tests/Models/NullWorkflowInstanceAbstractTest.php b/tests/Models/NullWorkflowInstanceAbstractTest.php
index 551a639..1518c56 100644
--- a/tests/Models/NullWorkflowInstanceAbstractTest.php
+++ b/tests/Models/NullWorkflowInstanceAbstractTest.php
@@ -47,6 +47,6 @@ final class NullWorkflowInstanceAbstractTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullWorkflowInstanceAbstract(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullWorkflowTemplateTest.php b/tests/Models/NullWorkflowTemplateTest.php
index db6be93..9fa6721 100644
--- a/tests/Models/NullWorkflowTemplateTest.php
+++ b/tests/Models/NullWorkflowTemplateTest.php
@@ -47,6 +47,6 @@ final class NullWorkflowTemplateTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullWorkflowTemplate(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }