using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        List<MarketModel> marketList = GetMarketList();

        var market = marketList.FirstOrDefault(m => m.Code.Equals("ABC"));

        Console.WriteLine("market is fetched");

        if (market is { Exchange: { } })

        {

            Console.WriteLine($"market is null");

        }

        Console.WriteLine("Done");

    }

    public class MarketModel

    {

        public ExchangeModel Exchange { get; set; }

        public long? ExchangeId { get; set; }

        public string Code { get; set; }

    }

    public class ExchangeModel

    {

        public long ExchangeId { get; set; }

        public string Name { get; set; }

    }

    private static List<MarketModel> GetMarketList()

    {

        return null;

        //return default(List<MarketModel>);

        //return new List<MarketModel>{};

        //return new List<MarketModel>{

        //  new MarketModel{ Exchange = new ExchangeModel{}},

        //};

    }

}