diff --git a/CarpentryWorkshop/CarpentryWorkshop/Forms/FormMaterialReplenishment.cs b/CarpentryWorkshop/CarpentryWorkshop/Forms/FormMaterialReplenishment.cs
index 5037445..e4d8bbb 100644
--- a/CarpentryWorkshop/CarpentryWorkshop/Forms/FormMaterialReplenishment.cs
+++ b/CarpentryWorkshop/CarpentryWorkshop/Forms/FormMaterialReplenishment.cs
@@ -1,5 +1,4 @@
 using CarpentryWorkshop.Entities;
-using CarpentryWorkshop.Entities.Enums;
 using CarpentryWorkshop.Repositories;
 
 namespace CarpentryWorkshop.Forms
@@ -34,7 +33,7 @@ namespace CarpentryWorkshop.Forms
         {
             InitializeComponent();
             _materialSpentRepository = materialSpentRepository ?? throw new ArgumentNullException(nameof(materialSpentRepository));
-            comboBoxMaterial.DataSource = materialRepository.ReadMaterials();
+            comboBoxMaterial.DataSource = materialRepository.ReadMaterials() ?? throw new ArgumentNullException(nameof(materialRepository));
             comboBoxMaterial.DisplayMember = "Name"; 
             comboBoxMaterial.ValueMember = "Id";
         }
diff --git a/CarpentryWorkshop/CarpentryWorkshop/Forms/FormProductMaterial.cs b/CarpentryWorkshop/CarpentryWorkshop/Forms/FormProductMaterial.cs
index 3c99b19..a5f8ec1 100644
--- a/CarpentryWorkshop/CarpentryWorkshop/Forms/FormProductMaterial.cs
+++ b/CarpentryWorkshop/CarpentryWorkshop/Forms/FormProductMaterial.cs
@@ -24,9 +24,9 @@ namespace CarpentryWorkshop.Forms
                     comboBoxProduct.SelectedItem = product.Type;
                     numericUpDownCount.Value = product.CountInWarehouse;
                     _productId = value;
+
                     dataGridView.Rows.Clear();
                     var rows = new List<DataGridViewRow>();
-
                     foreach (var productMaterial in product.ProductMaterial)
                     {
                         var material = _materialRepository.ReadMaterialById(productMaterial.MaterialId);