fix: normalize empty string SKU to nil/NULL to prevent unique key constraint violations on duplicate empty SKUs

controllers/product_controller.go

@@ -374,6 +374,10 @@ func CreateProduct(c *gin.Context) {
 		return
 	}
 
+	if req.SKU != nil && *req.SKU == "" {
+		req.SKU = nil
+	}
+
 	// Verifikasi SKU jika diisi
 	if req.SKU != nil && *req.SKU != "" {
 		var count int64
@@ -424,6 +428,10 @@ func UpdateProduct(c *gin.Context) {
 		return
 	}
 
+	if req.SKU != nil && *req.SKU == "" {
+		req.SKU = nil
+	}
+
 	var product models.Product
 	if err := config.DB.Where("id = ? AND company_id = ?", productID, *user.CompanyID).First(&product).Error; err != nil {
 		c.JSON(http.StatusNotFound, gin.H{"detail": "Produk tidak ditemukan"})
@@ -431,14 +439,18 @@ func UpdateProduct(c *gin.Context) {
 	}
 
 	// Verifikasi SKU jika berubah
-	if req.SKU != nil && *req.SKU != "" && (product.SKU == nil || *product.SKU != *req.SKU) {
-		var count int64
-		config.DB.Model(&models.Product{}).Where("sku = ? AND id != ?", *req.SKU, productID).Count(&count)
-		if count > 0 {
-			c.JSON(http.StatusBadRequest, gin.H{"detail": fmt.Sprintf("Produk dengan SKU '%s' sudah ada", *req.SKU)})
-			return
+	if req.SKU != nil && *req.SKU != "" {
+		if product.SKU == nil || *product.SKU != *req.SKU {
+			var count int64
+			config.DB.Model(&models.Product{}).Where("sku = ? AND id != ?", *req.SKU, productID).Count(&count)
+			if count > 0 {
+				c.JSON(http.StatusBadRequest, gin.H{"detail": fmt.Sprintf("Produk dengan SKU '%s' sudah ada", *req.SKU)})
+				return
+			}
+			product.SKU = req.SKU
 		}
-		product.SKU = req.SKU
+	} else {
+		product.SKU = nil
 	}
 
 	product.Name = req.Name