Why it's gives me a "An unhandled exception of type 'System.NullReferenceException' occurred in IP.dll"?

[NETANEL.S]

using System;
using System.Collections.Generic;
using System.Linq;
using System.ServiceModel;
using System.ServiceModel.Channels;
using System.Web;

namespace IP
{
    public class a
    {
        
                    public string GETip()
        {
            OperationContext context = OperationContext.Current;
            MessageProperties properties = context.IncomingMessageProperties;
            RemoteEndpointMessageProperty endpoint = properties[RemoteEndpointMessageProperty.Name] as RemoteEndpointMessageProperty;
            string address = string.Empty;
            //http://www.simosh.com/article/ddbggghj-get-client-ip-address-using-wcf-4-5-remoteendpointmessageproperty-in-load-balanc.html
            if (properties.Keys.Contains(HttpRequestMessageProperty.Name))
            {
                HttpRequestMessageProperty endpointLoadBalancer = properties[HttpRequestMessageProperty.Name] as HttpRequestMessageProperty;
                if (endpointLoadBalancer != null && endpointLoadBalancer.Headers["X-Forwarded-For"] != null)
                    address = endpointLoadBalancer.Headers["X-Forwarded-For"];
            }
            if (string.IsNullOrEmpty(address))
            {
                address = endpoint.Address;
            }
            return address;

        }

        }
    }

 

[jmcilhinney]

Please specify which line the exception is thrown on and provide the stack trace for the exception. Also, if you get a NullReferenceException, you should be checking that line to see which reference is null before posting. Once you know that, you may even be able to solve the issue for yourself.