using System;

using System.Collections.Generic;

using System.Collections.Immutable;

using System.Linq;

​

public static class Program {

​

    private static readonly ImmutableDictionary<string, Action> CommandMap

        = new Dictionary<string, Action>()

        {

            ["help"] = () => PrintHelp(),

            ["quit"] = () => ExitProgram(),

            ["shutdown"] = () => ShutdownSystem(),

        }.ToImmutableDictionary();

​

    private static void PrintHelp() => Console.WriteLine($"{nameof(PrintHelp)}");

    private static void ExitProgram() => Console.WriteLine($"{nameof(ExitProgram)}");

    private static void ShutdownSystem() => Console.WriteLine($"{nameof(ShutdownSystem)}");

​

    private static IEnumerable<string> CommandList { get; }

        = new[] { "help", "reboot", "shutdown" };

​

    private static void FixMe()

    {

        var list = CommandList.SelectMany(n => CommandMap.TryGetValue(n, out var action)

                                          ? new[] { action }

                                          : Enumerable.Empty<Action>());

        // The next is also fine, but the number of elements differs:

        //

        // var list = CommandList.Select(n => CommandMap.TryGetValue(n, out var action)

        //     ? action

        //     : () => {});

​

        foreach (var action in list)

        {

            action();

        }

    }

​

    public static void Main(string[] args)

    {

        FixMe();

    }

}

​