using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var xx = new List<int>{1};

        var yy = new List<int?>{};

        var zz = new List<int?>{1};

        Console.WriteLine(GetValue<int?>(1));//return 1

        Console.WriteLine(GetValue<int>(xx));//return 1

        Console.WriteLine(GetValue<long>(xx));//return 1

        Console.WriteLine(GetValue<int?>(xx));//return 1

        Console.WriteLine(GetValue<long?>(xx));//return 1

        Console.WriteLine(GetValue<int>(yy));//return 0

        Console.WriteLine(GetValue<long>(yy));//return 0

        Console.WriteLine(GetValue<int?>(yy));//return null

        Console.WriteLine(GetValue<long?>(yy));//return null

        Console.WriteLine(GetValue<int>(zz));//return 1

        Console.WriteLine(GetValue<long>(zz));//return 1

        Console.WriteLine(GetValue<int?>(zz));//return 1

        Console.WriteLine(GetValue<long>(zz));//return 1

    }

    public static T GetValue<T>(object value)

    {

        if (value == null || value == DBNull.Value)

        {

            return default(T);

        }

        else if (value.GetType().IsGenericType && value.GetType().GetGenericTypeDefinition().Equals(typeof(List<>)))

        {

            var list = ((System.Collections.IList)value).Cast<object>();

            if (!list.Any())

                return default(T);

            return GetValue<T>(list.Single());

        }

        else

        {

            var type = typeof(T);

            if (type.IsGenericType && type.GetGenericTypeDefinition().Equals(typeof(Nullable<>)))

            {                   

                if (value == null) 

                { 

                    return default(T); 

                }

                type = Nullable.GetUnderlyingType(type);

            }           

            return (T)Convert.ChangeType(value, type);

        }

    }

​

}