diff --git a/tests/Models/NullItemRelationTest.php b/tests/Models/NullItemRelationTest.php
index 8b9d183..757a550 100644
--- a/tests/Models/NullItemRelationTest.php
+++ b/tests/Models/NullItemRelationTest.php
@@ -47,6 +47,6 @@ final class NullItemRelationTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullItemRelation(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullItemRelationTypeTest.php b/tests/Models/NullItemRelationTypeTest.php
index 662c764..908ece4 100644
--- a/tests/Models/NullItemRelationTypeTest.php
+++ b/tests/Models/NullItemRelationTypeTest.php
@@ -47,6 +47,6 @@ final class NullItemRelationTypeTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullItemRelationType(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullItemTest.php b/tests/Models/NullItemTest.php
index 6f890da..3c1260f 100755
--- a/tests/Models/NullItemTest.php
+++ b/tests/Models/NullItemTest.php
@@ -47,6 +47,6 @@ final class NullItemTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullItem(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }