diff --git a/tests/Models/NullDepartmentTest.php b/tests/Models/NullDepartmentTest.php
index ed26f23..8bd8e89 100755
--- a/tests/Models/NullDepartmentTest.php
+++ b/tests/Models/NullDepartmentTest.php
@@ -39,4 +39,14 @@ final class NullDepartmentTest extends \PHPUnit\Framework\TestCase
         $null = new NullDepartment(2);
         self::assertEquals(2, $null->id);
     }
+
+    /**
+     * @covers Modules\Organization\Models\NullDepartment
+     * @group module
+     */
+    public function testJsonSerialize() : void
+    {
+        $null = new NullDepartment(2);
+        self::assertEquals(['id' => 2], $null);
+    }
 }
diff --git a/tests/Models/NullPositionTest.php b/tests/Models/NullPositionTest.php
index c67698f..54b0af6 100755
--- a/tests/Models/NullPositionTest.php
+++ b/tests/Models/NullPositionTest.php
@@ -39,4 +39,14 @@ final class NullPositionTest extends \PHPUnit\Framework\TestCase
         $null = new NullPosition(2);
         self::assertEquals(2, $null->id);
     }
+
+    /**
+     * @covers Modules\Organization\Models\NullPosition
+     * @group module
+     */
+    public function testJsonSerialize() : void
+    {
+        $null = new NullPosition(2);
+        self::assertEquals(['id' => 2], $null);
+    }
 }
diff --git a/tests/Models/NullUnitTest.php b/tests/Models/NullUnitTest.php
index d5942cc..79773f0 100755
--- a/tests/Models/NullUnitTest.php
+++ b/tests/Models/NullUnitTest.php
@@ -39,4 +39,14 @@ final class NullUnitTest extends \PHPUnit\Framework\TestCase
         $null = new NullUnit(2);
         self::assertEquals(2, $null->id);
     }
+
+    /**
+     * @covers Modules\Organization\Models\NullUnit
+     * @group module
+     */
+    public function testJsonSerialize() : void
+    {
+        $null = new NullUnit(2);
+        self::assertEquals(['id' => 2], $null);
+    }
 }