diff --git a/tests/Models/NullEmployeeEducationHistoryTest.php b/tests/Models/NullEmployeeEducationHistoryTest.php
index 628ff66..046ce01 100755
--- a/tests/Models/NullEmployeeEducationHistoryTest.php
+++ b/tests/Models/NullEmployeeEducationHistoryTest.php
@@ -47,6 +47,6 @@ final class NullEmployeeEducationHistoryTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullEmployeeEducationHistory(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullEmployeeHistoryTest.php b/tests/Models/NullEmployeeHistoryTest.php
index f62b495..7e156bb 100755
--- a/tests/Models/NullEmployeeHistoryTest.php
+++ b/tests/Models/NullEmployeeHistoryTest.php
@@ -47,6 +47,6 @@ final class NullEmployeeHistoryTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullEmployeeHistory(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullEmployeeTest.php b/tests/Models/NullEmployeeTest.php
index bc74c7e..0dde9ee 100755
--- a/tests/Models/NullEmployeeTest.php
+++ b/tests/Models/NullEmployeeTest.php
@@ -47,6 +47,6 @@ final class NullEmployeeTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullEmployee(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }
diff --git a/tests/Models/NullEmployeeWorkHistoryTest.php b/tests/Models/NullEmployeeWorkHistoryTest.php
index 6c44481..ff8f4f3 100755
--- a/tests/Models/NullEmployeeWorkHistoryTest.php
+++ b/tests/Models/NullEmployeeWorkHistoryTest.php
@@ -47,6 +47,6 @@ final class NullEmployeeWorkHistoryTest extends \PHPUnit\Framework\TestCase
     public function testJsonSerialize() : void
     {
         $null = new NullEmployeeWorkHistory(2);
-        self::assertEquals(['id' => 2], $null);
+        self::assertEquals(['id' => 2], $null->jsonSerialize());
     }
 }