diff --git a/Admin/Install/Navigation.php b/Admin/Install/Navigation.php
index 6c9ef15..635eef7 100644
--- a/Admin/Install/Navigation.php
+++ b/Admin/Install/Navigation.php
@@ -36,7 +36,7 @@ class Navigation
      *
      * @since  1.0.0
      */
-    public static function install(string $path = null, DatabasePool $dbPool = null) : void
+    public static function install(string $path, DatabasePool $dbPool) : void
     {
         \Modules\Navigation\Admin\Installer::installExternal($dbPool, ['path' => __DIR__ . '/Navigation.install.json']);
     }
diff --git a/Controller/BackendController.php b/Controller/BackendController.php
index a5cba5b..eafae99 100644
--- a/Controller/BackendController.php
+++ b/Controller/BackendController.php
@@ -15,6 +15,7 @@ declare(strict_types=1);
 namespace Modules\ItemManagement\Controller;
 
 use Modules\ItemManagement\Models\ItemMapper;
+
 use phpOMS\Contract\RenderableInterface;
 use phpOMS\Message\RequestAbstract;
 use phpOMS\Message\ResponseAbstract;
@@ -40,7 +41,7 @@ final class BackendController extends Controller
      * @since  1.0.0
      * @codeCoverageIgnore
      */
-    public function viewItemManagementSalesList(RequestAbstract $request, ResponseAbstract $response, $data = null) : \Serializable
+    public function viewItemManagementSalesList(RequestAbstract $request, ResponseAbstract $response, $data = null) : RenderableInterface
     {
         $view = new View($this->app, $request, $response);
         $view->setTemplate('/Modules/ItemManagement/Theme/Backend/sales-item-list');
@@ -62,7 +63,7 @@ final class BackendController extends Controller
      * @since  1.0.0
      * @codeCoverageIgnore
      */
-    public function viewItemManagementPurchaseList(RequestAbstract $request, ResponseAbstract $response, $data = null) : \Serializable
+    public function viewItemManagementPurchaseList(RequestAbstract $request, ResponseAbstract $response, $data = null) : RenderableInterface
     {
         $view = new View($this->app, $request, $response);
         $view->setTemplate('/Modules/ItemManagement/Theme/Backend/purchase-item-list');
@@ -81,7 +82,7 @@ final class BackendController extends Controller
      * @since  1.0.0
      * @codeCoverageIgnore
      */
-    public function viewItemManagementWarehousingList(RequestAbstract $request, ResponseAbstract $response, $data = null) : \Serializable
+    public function viewItemManagementWarehousingList(RequestAbstract $request, ResponseAbstract $response, $data = null) : RenderableInterface
     {
         $view = new View($this->app, $request, $response);
         $view->setTemplate('/Modules/ItemManagement/Theme/Backend/stock-list');
@@ -100,7 +101,7 @@ final class BackendController extends Controller
      * @since  1.0.0
      * @codeCoverageIgnore
      */
-    public function viewItemManagementSalesCreate(RequestAbstract $request, ResponseAbstract $response, $data = null) : \Serializable
+    public function viewItemManagementSalesCreate(RequestAbstract $request, ResponseAbstract $response, $data = null) : RenderableInterface
     {
         $view = new View($this->app, $request, $response);
         $view->setTemplate('/Modules/ItemManagement/Theme/Backend/item-create');
@@ -119,7 +120,7 @@ final class BackendController extends Controller
      * @since  1.0.0
      * @codeCoverageIgnore
      */
-    public function viewItemManagementPurchaseCreate(RequestAbstract $request, ResponseAbstract $response, $data = null) : \Serializable
+    public function viewItemManagementPurchaseCreate(RequestAbstract $request, ResponseAbstract $response, $data = null) : RenderableInterface
     {
         $view = new View($this->app, $request, $response);
         $view->setTemplate('/Modules/ItemManagement/Theme/Backend/item-create');
@@ -138,7 +139,7 @@ final class BackendController extends Controller
      * @since  1.0.0
      * @codeCoverageIgnore
      */
-    public function viewItemManagementWarehousingCreate(RequestAbstract $request, ResponseAbstract $response, $data = null) : \Serializable
+    public function viewItemManagementWarehousingCreate(RequestAbstract $request, ResponseAbstract $response, $data = null) : RenderableInterface
     {
         $view = new View($this->app, $request, $response);
         $view->setTemplate('/Modules/ItemManagement/Theme/Backend/item-create');
diff --git a/Models/ItemMapper.php b/Models/ItemMapper.php
index ee2b4d2..3f6df93 100644
--- a/Models/ItemMapper.php
+++ b/Models/ItemMapper.php
@@ -49,7 +49,7 @@ final class ItemMapper extends DataMapperAbstract
     protected static $primaryField = 'itemmgmt_item_id';    /**
      * Has many relation.
      *
-     * @var array<string, array<string, string>>
+     * @var array<string, array<string, null|string>>
      * @since 1.0.0
      */
     protected static $hasMany = [