Hello Pravesh Singh!
Below I Provide you a demo code for user define exception class.

using System;
namespace MindstickCustomeExceptionDemo
{
    public class MindstickEmployeeListNotFoundException : Exception
    {
        public MindstickEmployeeListNotFoundException()
        {
        }
        public MindstickEmployeeListNotFoundException(string message)
            : base(message)
        {
        }
    }
    class CustomException
    {
        static void Main(string[] args)
        {
            try
            {
                throw new MindstickEmployeeListNotFoundException("\n\n::Mindstick Employee List not found::\n\n");
            }
            catch (MindstickEmployeeListNotFoundException ce)
            {
                Console.WriteLine(ce.ToString());
            }
            Console.ReadKey();
        }
    }
}

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