Session is null problem in Handler-C#

System.Web.SessionState.IRequiresSessionState
  

Add this red line in your code as same as in example given below:

<%@ WebHandler Language="C#" Class="Handler" %>

using System;
using System.Web;

public class Handler : IHttpHandler, System.Web.SessionState.IRequiresSessionState
{
    public void ProcessRequest(HttpContext context)
    {
        context.Session["abc"] = "ankit";    // use session
    }
    public bool IsReusable
    {
        get
        {
            return false;
        }
    } 
}