Linq，如何选择联接的表中甚至有null的地方，C# windows窗体

using System;
using System.Linq;

// 定义一个数据模型类
public class Customer
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Order
{
    public int Id { get; set; }
    public int CustomerId { get; set; }
    public string Product { get; set; }
}

public class Program
{
    public static void Main()
    {
        // 模拟数据库中的数据
        var customers = new[]
        {
            new Customer { Id = 1, Name = "Customer 1" },
            new Customer { Id = 2, Name = "Customer 2" },
            new Customer { Id = 3, Name = "Customer 3" }
        };

        var orders = new[]
        {
            new Order { Id = 1, CustomerId = 1, Product = "Product 1" },
            new Order { Id = 2, CustomerId = 2, Product = "Product 2" },
            new Order { Id = 3, CustomerId = 3, Product = "Product 3" },
            new Order { Id = 4, CustomerId = 4, Product = "Product 4" } // 模拟一个不存在的CustomerId
        };

        // 使用Linq进行左联接查询
        var query = from customer in customers
                    join order in orders on customer.Id equals order.CustomerId into gj
                    from subOrder in gj.DefaultIfEmpty()
                    select new
                    {
                        CustomerName = customer.Name,
                        ProductName = subOrder?.Product ?? "No Order" // 处理null值
                    };

        // 输出查询结果
        foreach (var result in query)
        {
            Console.WriteLine($"Customer: {result.CustomerName}, Product: {result.ProductName}");
        }
    }
}