diff --git a/NorthwindCRUD/Models/Contracts/IAddress.cs b/NorthwindCRUD/Models/Contracts/IAddress.cs
index 5d9a55c..40ace5e 100644
--- a/NorthwindCRUD/Models/Contracts/IAddress.cs
+++ b/NorthwindCRUD/Models/Contracts/IAddress.cs
@@ -4,15 +4,15 @@ namespace NorthwindCRUD.Models.Contracts
 {
     public interface IAddress
     {
-        string Street { get; set; }
+        string? Street { get; set; }
 
-        string City { get; set; }
+        string? City { get; set; }
 
-        string Region { get; set; }
+        string? Region { get; set; }
 
-        string PostalCode { get; set; }
+        string? PostalCode { get; set; }
 
-        string Country { get; set; }
+        string? Country { get; set; }
 
         string? Phone { get; set; }
     }
diff --git a/NorthwindCRUD/Models/DbModels/AddressDb.cs b/NorthwindCRUD/Models/DbModels/AddressDb.cs
index 527ebb9..72b3e51 100644
--- a/NorthwindCRUD/Models/DbModels/AddressDb.cs
+++ b/NorthwindCRUD/Models/DbModels/AddressDb.cs
@@ -10,15 +10,15 @@ public class AddressDb : IAddress
         [DatabaseGenerated(DatabaseGeneratedOption.None)]
         public string AddressId { get; set; }
 
-        public string Street { get; set; }
+        public string? Street { get; set; }
 
-        public string City { get; set; }
+        public string? City { get; set; }
 
-        public string Region { get; set; }
+        public string? Region { get; set; }
 
-        public string PostalCode { get; set; }
+        public string? PostalCode { get; set; }
 
-        public string Country { get; set; }
+        public string? Country { get; set; }
 
         public string? Phone { get; set; }
 
diff --git a/NorthwindCRUD/Models/Dtos/AddressDto.cs b/NorthwindCRUD/Models/Dtos/AddressDto.cs
index 10bc810..2766983 100644
--- a/NorthwindCRUD/Models/Dtos/AddressDto.cs
+++ b/NorthwindCRUD/Models/Dtos/AddressDto.cs
@@ -5,27 +5,22 @@ namespace NorthwindCRUD.Models.Dtos
 {
     public class AddressDto : IAddress
     {
-        [Required(ErrorMessage = "Street is required.")]
         [StringLength(100, ErrorMessage = "Street cannot exceed 100 characters.")]
-        public string Street { get; set; }
+        public string? Street { get; set; }
 
-        [Required(ErrorMessage = "City is required.")]
         [StringLength(50, ErrorMessage = "City cannot exceed 50 characters.")]
-        public string City { get; set; }
+        public string? City { get; set; }
 
-        [Required(ErrorMessage = "Region is required.")]
         [StringLength(50, ErrorMessage = "Region cannot exceed 50 characters.")]
-        public string Region { get; set; }
+        public string? Region { get; set; }
 
-        [Required(ErrorMessage = "PostalCode is required.")]
         [StringLength(20, ErrorMessage = "Postal code cannot exceed 20 characters.")]
-        public string PostalCode { get; set; }
+        public string? PostalCode { get; set; }
 
-        [Required(ErrorMessage = "Country is required.")]
         [StringLength(50, ErrorMessage = "Country cannot exceed 50 characters.")]
-        public string Country { get; set; }
+        public string? Country { get; set; }
 
-        [RegularExpression(@"^\+?[1-9]\d{1,14}$", ErrorMessage = "Phone number is not valid.")]
+        [RegularExpression(@"^\+?[0-9][0-9\-]{1,14}$", ErrorMessage = "Phone number is not valid.")]
         public string? Phone { get; set; }
     }
 }
diff --git a/NorthwindCRUD/Services/SalesService.cs b/NorthwindCRUD/Services/SalesService.cs
index 8f0dffc..14e2145 100644
--- a/NorthwindCRUD/Services/SalesService.cs
+++ b/NorthwindCRUD/Services/SalesService.cs
@@ -71,7 +71,7 @@ public SalesDto[] RetrieveSalesDataByCountry(string startDate, string endDate, s
             .ToList();
 
             var filteredData = salesData
-            .Where(od => od.Order.ShipAddress?.Country.ToLower(CultureInfo.InvariantCulture) == normalizedCountry && DateTime.Parse(od.Order.OrderDate, CultureInfo.InvariantCulture) >= parsedStartDate && DateTime.Parse(od.Order.RequiredDate, CultureInfo.InvariantCulture) <= parsedEndDate)
+            .Where(od => od.Order.ShipAddress?.Country?.ToLower(CultureInfo.InvariantCulture) == normalizedCountry && DateTime.Parse(od.Order.OrderDate, CultureInfo.InvariantCulture) >= parsedStartDate && DateTime.Parse(od.Order.RequiredDate, CultureInfo.InvariantCulture) <= parsedEndDate)
             .ToList();
 
             var sales = filteredData.Select(od => new SalesDto