CSharp: null object Pattern in donet 6

/// <summary>
    /// 空对象模式 null object Pattern
    ///
    /// </summary>
    public abstract class Application
    {
 
        /// <summary>
        ///
        /// </summary>
        private static readonly NullApplication NullApplication = new NullApplication();
        /// <summary>
        ///
        /// </summary>
        /// <param name="processId"></param>
        public Application(Guid processId)
        {
            ProcessId = processId;
        }
        /// <summary>
        ///
        /// </summary>
        public static NullApplication Default
        {
            get
            {
                return NullApplication;
            }
        }
        /// <summary>
        ///
        /// </summary>
        public abstract string Name { get; }
        /// <summary>
        ///
        /// </summary>
        public Guid ProcessId { get; }
        /// <summary>
        ///
        /// </summary>
        public virtual void Open()
        {
            Console.WriteLine($"应用程序 {Name} 已经打开.");
        }
        /// <summary>
        ///
        /// </summary>
        public virtual void Close()
        {
            Console.WriteLine($"应用程序 {Name} 已经关闭.");
        }
    }
 
 
 
    /// <summary>
    /// 空对象模式 null object Pattern
    /// </summary>
    public class NullApplication : Application
    {
 
        /// <summary>
        ///
        /// </summary>
        public NullApplication()
            : base(Guid.Empty)
        {
        }
        /// <summary>
        ///
        /// </summary>
        public override string Name => string.Empty;
        /// <summary>
        ///
        /// </summary>
        public override void Open()
        {
        }
        /// <summary>
        ///
        /// </summary>
        public override void Close()
        {
        }
    }
 
 
    /// <summary>
    ///
    /// </summary>
    public class Gmail : Application
    {
 
        /// <summary>
        ///
        /// </summary>
        /// <param name="processId"></param>
        public Gmail(Guid processId)
            : base(processId)
        {
        }
        /// <summary>
        ///
        /// </summary>
        public override string Name => "Gmail";
    }
 
   /// <summary>
    ///
    /// </summary>
    public class SubwaySurfers : Application
    {
 
        /// <summary>
        ///
        /// </summary>
        /// <param name="processId"></param>
        public SubwaySurfers(Guid processId)
            : base(processId)
        {
        }
        /// <summary>
        ///
        /// </summary>
        public override string Name => "Subway Surfers";
    }
 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Geovin.Du.DuNullObject.Applications.Common;
 
 
namespace Geovin.Du.DuNullObject.Applications
{
 
    /// <summary>
    ///
    /// </summary>
    public class GeovinDu : Application
    {
 
        /// <summary>
        ///
        /// </summary>
        /// <param name="processId"></param>
        public GeovinDu(Guid processId)
            : base(processId)
        {
        }
        /// <summary>
        ///
        /// </summary>
        public override string Name => "GeovinDu";
    }
}
 
   /// <summary>
    ///
    /// </summary>
    public class ApplicationRepository
    {
 
        /// <summary>
        ///
        /// </summary>
        private readonly Dictionary<Guid, Application> _installedApplications;
 
 
        /// <summary>
        ///
        /// </summary>
        public ApplicationRepository()
        {
            var gmailProcessId = new Guid("6a3852ab-0973-4d1b-82d8-edd131c5f0a9");
            var subwaySurfersProcessId = new Guid("c8bc60c6-f1d2-484f-91ee-a6e6dec9e782");
            var geovinduProcessId = new Guid("2b8ba9a3-4f83-4f86-96a8-94daf79fa4bd");
 
            _installedApplications = new Dictionary<Guid, Application>
            {
                { gmailProcessId, new Gmail(gmailProcessId) },
                { subwaySurfersProcessId, new SubwaySurfers(subwaySurfersProcessId) },
                { geovinduProcessId, new GeovinDu(geovinduProcessId) },
            };
        }
        /// <summary>
        ///
        /// </summary>
        /// <param name="processId"></param>
        /// <returns></returns>
        public Application Find(Guid processId)
        {
            if (_installedApplications.TryGetValue(processId, out Application application))
            {
                return application;
            }
 
            return Application.Default;
        }
    }
 
    /// <summary>
    /// 空对象模式 null object Pattern
    /// geovindu,Geovin Du,涂聚文
    /// </summary>
    public static class SmartphoneApplicationExecutor
    {
 
        /// <summary>
        ///
        /// </summary>
        public static void Execute()
        {
 
            ConsoleExtension.WriteSeparator("小手机应用程序 Demo");
 
            var applicationRepository = new ApplicationRepository();
 
            var validProcessId = new Guid("6a3852ab-0973-4d1b-82d8-edd131c5f0a9");
            var invalidProcessId = Guid.Empty;
 
            var gmail = applicationRepository.Find(validProcessId);
            gmail.Open();
            gmail.Close();
 
            // Null exception won't be thrown if an application with the specified process ID can't be found.
            // In that case, default (NULL) object will be returned.
            var geovindu = applicationRepository.Find(invalidProcessId);
            geovindu.Open();
            geovindu.Close();
        }
    }

Console.WriteLine("Hello, Geovin Du! 学习 .net 6 ");
//Geovin.Du.DuEmail.EmailExecutor.Execute();
//Geovin.Du.DuStock.StockExecutor.Execute();
// Geovin.Du.DuShoppingCart.ShoppingCartExecutor.Execute();
Geovin.Du.DuNullObject.SmartphoneApplicationExecutor.Execute();

Hello, Geovin Du! 学习 .net 6
 
小手机应用程序 Demo
--------------------------------------------------
应用程序 Gmail 已经打开.
应用程序 Gmail 已经关闭.