Fixed issue "Failing to instantiate CreateCustomerCommandHandler"

Northwind.Application/Interfaces/INotificationService.cs

@@ -1,9 +1,10 @@
 using Northwind.Application.Notifications.Models;
+using System.Threading.Tasks;
 
 namespace Northwind.Application.Interfaces
 {
     public interface INotificationService
     {
-        void Send(Message message);
+        Task SendAsync(Message message);
     }
 }

Northwind.Infrastructure/NotificationService.cs

@@ -1,13 +1,14 @@
 using Northwind.Application.Interfaces;
 using Northwind.Application.Notifications.Models;
+using System.Threading.Tasks;
 
 namespace Northwind.Infrastructure
 {
     public class NotificationService : INotificationService
     {
-        public void Send(Message message)
+        public Task SendAsync(Message message)
         {
-            // Do nothing
+            return Task.CompletedTask;
         }
     }
 }

Northwind.WebUI/Startup.cs

@@ -4,13 +4,15 @@
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Mvc;
-using Microsoft.AspNetCore.SpaServices.AngularCli;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Northwind.Application.Customers.Commands.CreateCustomer;
 using Northwind.Application.Infrastructure;
+using Northwind.Application.Interfaces;
 using Northwind.Application.Products.Queries.GetProduct;
+using Northwind.Common;
+using Northwind.Infrastructure;
 using Northwind.Persistence;
 using Northwind.WebUI.Filters;
 using NSwag.AspNetCore;
@@ -31,6 +33,9 @@ public Startup(IConfiguration configuration)
         public void ConfigureServices(IServiceCollection services)
         {
             // Add framework services.
+            services.AddTransient<INotificationService, NotificationService>();
+            services.AddTransient<IDateTime, MachineDateTime>();
+
             // Add MediatR
             services.AddTransient(typeof(IPipelineBehavior<,>), typeof(RequestPreProcessorBehavior<,>));
             services.AddTransient(typeof(IPipelineBehavior<,>), typeof(RequestPerformanceBehaviour<,>));
@@ -41,7 +46,6 @@ public void ConfigureServices(IServiceCollection services)
             services.AddDbContext<NorthwindDbContext>(options =>
                 options.UseSqlServer(Configuration.GetConnectionString("NorthwindDatabase")));
 
-
             services
                 .AddMvc(options => options.Filters.Add(typeof(CustomExceptionFilterAttribute)))
                 .SetCompatibilityVersion(CompatibilityVersion.Version_2_1)