diff --git a/tests/Models/NullProjectAttributeTest.php b/tests/Models/NullProjectAttributeTest.php
index 8306bfe..a5e1c1d 100644
--- a/tests/Models/NullProjectAttributeTest.php
+++ b/tests/Models/NullProjectAttributeTest.php
@@ -47,6 +47,6 @@ final class NullProjectAttributeTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullProjectAttribute(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullProjectAttributeTypeTest.php b/tests/Models/NullProjectAttributeTypeTest.php
index 56e7850..f07dd92 100644
--- a/tests/Models/NullProjectAttributeTypeTest.php
+++ b/tests/Models/NullProjectAttributeTypeTest.php
@@ -47,6 +47,6 @@ final class NullProjectAttributeTypeTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullProjectAttributeType(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullProjectAttributeValueTest.php b/tests/Models/NullProjectAttributeValueTest.php
index 2a2b3e5..09cc702 100644
--- a/tests/Models/NullProjectAttributeValueTest.php
+++ b/tests/Models/NullProjectAttributeValueTest.php
@@ -47,6 +47,6 @@ final class NullProjectAttributeValueTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullProjectAttributeValue(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullProjectTest.php b/tests/Models/NullProjectTest.php
index 77244d2..845622a 100755
--- a/tests/Models/NullProjectTest.php
+++ b/tests/Models/NullProjectTest.php
@@ -47,6 +47,6 @@ final class NullProjectTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullProject(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }