diff --git a/Microservice.Customer.Api.Test.Unit/GetCustomerMediatrTests.cs b/Microservice.Customer.Api.Test.Unit/GetCustomerMediatrTests.cs
index bd0b69c..2e21c64 100644
--- a/Microservice.Customer.Api.Test.Unit/GetCustomerMediatrTests.cs
+++ b/Microservice.Customer.Api.Test.Unit/GetCustomerMediatrTests.cs
@@ -15,10 +15,10 @@ namespace Microservice.Customer.Api.Test.Unit;
 [TestFixture]
 public class GetCustomerMediatrTests
 {
-    private Mock<ICustomerRepository> customerRepositoryMock = new();
-    private Mock<ICustomerHttpAccessor> customerHttpAccessorMock = new();
-    private Mock<ILogger<GetCustomerQueryHandler>> loggerMock = new();
-    private ServiceCollection services = new();
+    private readonly Mock<ICustomerRepository> customerRepositoryMock = new();
+    private readonly Mock<ICustomerHttpAccessor> customerHttpAccessorMock = new();
+    private readonly Mock<ILogger<GetCustomerQueryHandler>> loggerMock = new();
+    private readonly ServiceCollection services = new();
     private ServiceProvider serviceProvider;
     private IMediator mediator;
 
@@ -60,7 +60,7 @@ public async Task Get_customer_return_customer()
 
         customerRepositoryMock
                 .Setup(x => x.ByIdAsync(customerId))
-                .Returns(Task.FromResult(customer));
+                .Returns(Task.FromResult(customer ?? null));
 
         var getCustomerRequest = new GetCustomerRequest(customerId);
 
diff --git a/Microservice.Customer.Api.Test.Unit/UpdateCustomerMediatrTests.cs b/Microservice.Customer.Api.Test.Unit/UpdateCustomerMediatrTests.cs
index 6a42770..d9d510f 100644
--- a/Microservice.Customer.Api.Test.Unit/UpdateCustomerMediatrTests.cs
+++ b/Microservice.Customer.Api.Test.Unit/UpdateCustomerMediatrTests.cs
@@ -1,3 +1,5 @@
+// Ignore Spelling: Mediatr
+
 using FluentValidation;
 using MediatR;
 using Microservice.Customer.Api.Data.Repository.Interfaces;
@@ -14,10 +16,10 @@ namespace Microservice.Customer.Api.Test.Unit;
 [TestFixture]
 public class UpdateCustomerMediatrTests
 {
-    private Mock<ICustomerRepository> customerRepositoryMock = new();
-    private Mock<ICustomerHttpAccessor> customerHttpAccessorMock = new();
-    private Mock<ILogger<UpdateCustomerCommandHandler>> loggerMock = new();
-    private ServiceCollection services = new();
+    private readonly Mock<ICustomerRepository> customerRepositoryMock = new();
+    private readonly Mock<ICustomerHttpAccessor> customerHttpAccessorMock = new();
+    private readonly Mock<ILogger<UpdateCustomerCommandHandler>> loggerMock = new();
+    private readonly ServiceCollection services = new();
     private ServiceProvider serviceProvider;
     private IMediator mediator;
     private Guid customerId;
@@ -59,25 +61,28 @@ public async Task Customer_updated_return_success_message()
     {
         var customerId = Guid.NewGuid();
 
-        var customer = new Domain.Customer() { Id = customerId, Email = "ValidEmail@hotmail.com", Surname = "TestSurname", FirstName = "TestFirstName" };
+        Domain.Customer? customer = new Domain.Customer() { Id = customerId, Email = "ValidEmail@hotmail.com", Surname = "TestSurname", FirstName = "TestFirstName" };
 
         customerHttpAccessorMock.Setup(x => x.CustomerId)
             .Returns(customerId);
 
         customerRepositoryMock
                 .Setup(x => x.ByIdAsync(customerId))
-                .Returns(Task.FromResult(customer));
+                .Returns(Task.FromResult(customer ?? null));
 
         customerRepositoryMock
                 .Setup(x => x.ExistsAsync(customerId))
                 .Returns(Task.FromResult(true));
 
-        customer.Surname = "Changed Surname";
-        customer.FirstName = "Changed FirstName";
-        customer.Email = "Changed Email";
+        if (customer is not null)
+        {
+            customer.Surname = "Changed Surname";
+            customer.FirstName = "Changed FirstName";
+            customer.Email = "Changed Email";
 
-        customerRepositoryMock
-                .Setup(x => x.UpdateAsync(customer));
+            customerRepositoryMock
+                    .Setup(x => x.UpdateAsync(customer));
+        }       
 
         var updateCustomerRequest = new UpdateCustomerRequest(customerId, "ValidEmail@hotmail.com", "TestSurname", "TestFirstName");
 
@@ -142,7 +147,7 @@ public void Customer_not_updated_invalid_email_return_exception_fail_message()
     }
 
     [Test]
-    public void Customer_not_updated_invalid_surname_firstname_return_exception_fail_message()
+    public void Customer_not_updated_invalid_surname_first_name_return_exception_fail_message()
     {
         customerRepositoryMock
                 .Setup(x => x.ExistsAsync("ValidEmail@hotmail.com"))
diff --git a/Microservice.Customer.Api/Data/Repository/CustomerRepository.cs b/Microservice.Customer.Api/Data/Repository/CustomerRepository.cs
index 36a036a..dca21d1 100644
--- a/Microservice.Customer.Api/Data/Repository/CustomerRepository.cs
+++ b/Microservice.Customer.Api/Data/Repository/CustomerRepository.cs
@@ -30,7 +30,7 @@ public async Task UpdateAsync(Domain.Customer entity)
         return await db.Customer.AsNoTracking().ToListAsync();
     }
 
-    public async Task<Domain.Customer> ByIdAsync(Guid id)
+    public async Task<Domain.Customer?> ByIdAsync(Guid id)
     {
         await using var db = await _dbContextFactory.CreateDbContextAsync();
         return await db.Customer.FindAsync(id);
diff --git a/Microservice.Customer.Api/Data/Repository/Interfaces/ICustomerRepository.cs b/Microservice.Customer.Api/Data/Repository/Interfaces/ICustomerRepository.cs
index 8d09f1d..16b223c 100644
--- a/Microservice.Customer.Api/Data/Repository/Interfaces/ICustomerRepository.cs
+++ b/Microservice.Customer.Api/Data/Repository/Interfaces/ICustomerRepository.cs
@@ -5,7 +5,7 @@ public interface ICustomerRepository
     Task<Domain.Customer> AddAsync(Domain.Customer customer);
     Task UpdateAsync(Domain.Customer entity);
     Task<IEnumerable<Domain.Customer>> AllAsync();
-    Task<Domain.Customer> ByIdAsync(Guid id);
+    Task<Domain.Customer?> ByIdAsync(Guid id);
     Task<bool> ExistsAsync(string email);
     Task<bool> ExistsAsync(string email, Guid id);
     Task<bool> ExistsAsync(Guid id);
diff --git a/Microservice.Customer.Api/Domain/Customer.cs b/Microservice.Customer.Api/Domain/Customer.cs
index 7da3b7b..70259b0 100644
--- a/Microservice.Customer.Api/Domain/Customer.cs
+++ b/Microservice.Customer.Api/Domain/Customer.cs
@@ -11,15 +11,15 @@ public class Customer
 
     [MaxLength(30)]
     [Required]
-    public string Surname { get; set; }
+    public string Surname { get; set; } = string.Empty;
 
     [MaxLength(30)]
     [Required]
-    public string FirstName { get; set; }
+    public string FirstName { get; set; } = string.Empty;
 
     [EmailAddress]
     [Required]
-    public string Email { get; set; }
+    public string Email { get; set; } = string.Empty;
 
     [Required]
     public DateTime Created { get; set; } = DateTime.Now;
diff --git a/Microservice.Customer.Api/Helpers/EnvironmentVariables.cs b/Microservice.Customer.Api/Helpers/EnvironmentVariables.cs
index 28a9139..98efe28 100644
--- a/Microservice.Customer.Api/Helpers/EnvironmentVariables.cs
+++ b/Microservice.Customer.Api/Helpers/EnvironmentVariables.cs
@@ -1,8 +1,10 @@
-namespace Microservice.Customer.Api.Helpers;
+// Ignore Spelling: Jwt
+
+namespace Microservice.Customer.Api.Helpers;
 
 public class EnvironmentVariables
 {
-    public static string JwtIssuer = Environment.GetEnvironmentVariable(Constants.JwtIssuer);
-    public static string JwtAudience = Environment.GetEnvironmentVariable(Constants.JwtAudience);
-    public static string JwtSymmetricSecurityKey = Environment.GetEnvironmentVariable(Constants.JwtSymmetricSecurityKey);
+    public static string JwtIssuer = Environment.GetEnvironmentVariable(Constants.JwtIssuer) ?? "Environment Variable JwtIssuer not found.";
+    public static string JwtAudience = Environment.GetEnvironmentVariable(Constants.JwtAudience) ?? "Environment Variable JwtAudience not found.";
+    public static string JwtSymmetricSecurityKey = Environment.GetEnvironmentVariable(Constants.JwtSymmetricSecurityKey) ?? "Environment Variable JwtSymmetricSecurityKey not found.";
 }
\ No newline at end of file
diff --git a/Microservice.Customer.Api/Mediatr/GetCustomer/GetCustomerQueryHandler.cs b/Microservice.Customer.Api/Mediatr/GetCustomer/GetCustomerQueryHandler.cs
index 86d82b6..9b3e41e 100644
--- a/Microservice.Customer.Api/Mediatr/GetCustomer/GetCustomerQueryHandler.cs
+++ b/Microservice.Customer.Api/Mediatr/GetCustomer/GetCustomerQueryHandler.cs
@@ -18,7 +18,7 @@ public async Task<GetCustomerResponse> Handle(GetCustomerRequest getCustomerRequ
         var customer = await _customerRepository.ByIdAsync(getCustomerRequest.Id);
         if (customer == null)
         {
-            _logger.LogError($"Customer not found - {getCustomerRequest.Id}");
+            _logger.LogError($"Customer not found - { getCustomerRequest.Id }");
             throw new NotFoundException("Customer not found.");
         }
 
diff --git a/Microservice.Customer.Api/Microservice.Customer.Api.csproj b/Microservice.Customer.Api/Microservice.Customer.Api.csproj
index f46a85b..dea68f1 100644
--- a/Microservice.Customer.Api/Microservice.Customer.Api.csproj
+++ b/Microservice.Customer.Api/Microservice.Customer.Api.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <TargetFramework>net8.0</TargetFramework>
-    <Nullable>disable</Nullable>
+    <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
     <InvariantGlobalization>false</InvariantGlobalization>
     <UserSecretsId>b2c27b2e-bd15-497f-93fa-fd78705e6a39</UserSecretsId>