I am getting error in the below code and i specified the error line

using System;
namespace wildert
{
    public class Metronome
    {
        public event TickHandler Tick;
        public EventArgs e = null;
        public delegate void TickHandler(Metronome m, EventArgs e);
        public void Start()
        {
            while (true)
            {
                System.Threading.Thread.Sleep(3000);
                if (Tick != null)
                {
                    Tick(this, e);
                }
            }
        }
    }
        public class Listener
        {
            public void Subscribe(Metronome m)
            {
            m.Tick += new Metronome.TickHandler(HeardIt);//I am getting error here
            }
            private void HeardIt(Metronome m, EventArgs e)
            {
                System.Console.WriteLine("HEARD IT");
            }

        }
    class Test
    {
        static void Main()
        {
            Metronome m = new Metronome();
            Listener l = new Listener();
            l.Subscribe(m);
            m.Start();
        }
    }
}