using System;

​

var e = new Event("123", null);

public class Event

{

  public string Id {get; private set;}

  public string Message {get; private set; }

​

  public Event(string id, string message)

  {

    if (id == null)

    {

        throw new ArgumentNullException("id");

    }

    if (message == null)

    {

        throw new ArgumentNullException("message");

    }  

    Id = id ?? throw new ArgumentNullException(nameof(id));

    Message = message ?? throw new ArgumentNullException(nameof(message));

  } 

}