diff --git a/tests/Models/NullKanbanBoardTest.php b/tests/Models/NullKanbanBoardTest.php
index 47305a3..3705714 100755
--- a/tests/Models/NullKanbanBoardTest.php
+++ b/tests/Models/NullKanbanBoardTest.php
@@ -47,6 +47,6 @@ final class NullKanbanBoardTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullKanbanBoard(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullKanbanCardCommentTest.php b/tests/Models/NullKanbanCardCommentTest.php
index f4e8ccd..a59ebd4 100755
--- a/tests/Models/NullKanbanCardCommentTest.php
+++ b/tests/Models/NullKanbanCardCommentTest.php
@@ -47,6 +47,6 @@ final class NullKanbanCardCommentTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullKanbanCardComment(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullKanbanCardTest.php b/tests/Models/NullKanbanCardTest.php
index 53165ff..54993f8 100755
--- a/tests/Models/NullKanbanCardTest.php
+++ b/tests/Models/NullKanbanCardTest.php
@@ -47,6 +47,6 @@ final class NullKanbanCardTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullKanbanCard(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullKanbanColumnTest.php b/tests/Models/NullKanbanColumnTest.php
index 9fd91f4..65facdd 100755
--- a/tests/Models/NullKanbanColumnTest.php
+++ b/tests/Models/NullKanbanColumnTest.php
@@ -47,6 +47,6 @@ final class NullKanbanColumnTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullKanbanColumn(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }