Simple Flash Message with C#

FlashMessage.cs

using System;
using System.Web;

namespace CMSApplication
{
    public class FlashMessage : System.Web.UI.Page
    {
        public void put(string key,string message = "")
        {
           Session[key] = message;
        }

        public string get(string key)
        {
            if(Session[key] == null)
            {
                return "";
            }else{
                string message = Session[key].ToString();
                Session.Remove(key);
                return message;
            }
        }
        public bool has(string key)
        {
            if(Session[key] == null)
            {
                return false;
            }else{
                return true;
            }
        }
    }    
}