diff --git a/tests/Models/NullContractTest.php b/tests/Models/NullContractTest.php
index f067b0b..e9aa160 100755
--- a/tests/Models/NullContractTest.php
+++ b/tests/Models/NullContractTest.php
@@ -47,6 +47,6 @@ final class NullContractTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullContract(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }