diff --git a/tests/Models/NullCollectionTest.php b/tests/Models/NullCollectionTest.php
index 703fcd6..824cc7a 100755
--- a/tests/Models/NullCollectionTest.php
+++ b/tests/Models/NullCollectionTest.php
@@ -47,6 +47,6 @@ final class NullCollectionTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullCollection(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullMediaContentTest.php b/tests/Models/NullMediaContentTest.php
index 1b84c0b..df3054b 100644
--- a/tests/Models/NullMediaContentTest.php
+++ b/tests/Models/NullMediaContentTest.php
@@ -47,6 +47,6 @@ final class NullMediaContentTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullMediaContent(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullMediaTest.php b/tests/Models/NullMediaTest.php
index 9ef8cd1..c81ed4e 100755
--- a/tests/Models/NullMediaTest.php
+++ b/tests/Models/NullMediaTest.php
@@ -47,6 +47,6 @@ final class NullMediaTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullMedia(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullMediaTypeTest.php b/tests/Models/NullMediaTypeTest.php
index fa8d631..bea4375 100755
--- a/tests/Models/NullMediaTypeTest.php
+++ b/tests/Models/NullMediaTypeTest.php
@@ -47,6 +47,6 @@ final class NullMediaTypeTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullMediaType(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullReferenceTest.php b/tests/Models/NullReferenceTest.php
index 5be554d..874fcbe 100644
--- a/tests/Models/NullReferenceTest.php
+++ b/tests/Models/NullReferenceTest.php
@@ -47,6 +47,6 @@ final class NullReferenceTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullReference(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }