diff --git a/tests/Models/NullCalendarTest.php b/tests/Models/NullCalendarTest.php
index f40a049..27e4e5b 100755
--- a/tests/Models/NullCalendarTest.php
+++ b/tests/Models/NullCalendarTest.php
@@ -47,6 +47,6 @@ final class NullCalendarTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullCalendar(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullEventTest.php b/tests/Models/NullEventTest.php
index e7bbc6a..534ed3c 100755
--- a/tests/Models/NullEventTest.php
+++ b/tests/Models/NullEventTest.php
@@ -47,6 +47,6 @@ final class NullEventTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullEvent(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullScheduleTest.php b/tests/Models/NullScheduleTest.php
index fab928d..af892bf 100755
--- a/tests/Models/NullScheduleTest.php
+++ b/tests/Models/NullScheduleTest.php
@@ -47,6 +47,6 @@ final class NullScheduleTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullSchedule(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }