diff --git a/tests/Models/NullDrawImageTest.php b/tests/Models/NullDrawImageTest.php
index 1e59729..8cd4993 100755
--- a/tests/Models/NullDrawImageTest.php
+++ b/tests/Models/NullDrawImageTest.php
@@ -47,6 +47,6 @@ final class NullDrawImageTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullDrawImage(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }