Html Helper for creating a link that enables sorting for the column

SortLinkExtensions.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Web.Helpers;
using System.Collections.Specialized;

namespace cflat
{
    public class SortOptions
    {
        public SortOptions()
        {
            this.Column = "";
            this.Direction = SortDirection.Ascending;
        }

        public string Column { get; set; }
        public SortDirection Direction { get; set; }
    }

    public static class SortLinkExtensions
    {
        public static MvcHtmlString SortLink(this HtmlHelper helper, string linkText, SortOptions sort = null, string column = null, object htmlAttributes = null)
        {
            return SortLink(helper, linkText, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes), sort, column);
        }

        public static MvcHtmlString SortLink(this HtmlHelper helper, string linkText, IDictionary<string, object> htmlAttributes, SortOptions sort = null, string column = null)
        {
            if (sort == null)
            {
                sort = LoadSortOptionsFromViewData(helper.ViewData);
            }

            string formattedColumnName = FormatColumnName(column ?? linkText); // use linkText if there is no column
            string updatedQs = BuildQueryString(helper.ViewContext.RequestContext.HttpContext.Request.QueryString, formattedColumnName, sort);
            TagBuilder anchor = new TagBuilder("a");

            anchor.MergeAttributes(htmlAttributes, false);

            anchor.MergeAttribute("href", "?" + updatedQs);

            anchor.SetInnerText(linkText);

            if (formattedColumnName == sort.Column)
            {
                anchor.MergeAttribute("class", "active" + " " + sort.Direction.ToString().ToLower());
            }

            return MvcHtmlString.Create(anchor.ToString());
        }

        private static SortOptions LoadSortOptionsFromViewData(ViewDataDictionary viewData)
        {
            object sortObj = null;
            if (!viewData.TryGetValue("Sort", out sortObj))
            {
                throw new InvalidOperationException("You must provide SortOptions, either via ViewData or param.");
            }

            return (SortOptions)sortObj;
        }

        static string FormatColumnName(string column)
        {
            if (string.IsNullOrWhiteSpace(column))
            {
                throw new InvalidOperationException("Column must have a value");
            }

            column = column.Substring(0, 1).ToUpper() + column.Substring(1);

            return column;
        }
    
        static string BuildQueryString(NameValueCollection queryString, string column, SortOptions sort)
        {
            System.Collections.Specialized.NameValueCollection qs = HttpUtility.ParseQueryString(queryString.ToString());
            qs.Remove("Column");
            qs.Add("Column", column);

            qs.Remove("Direction");
            if (sort.Column == column)
            {
                SortDirection dir = sort.Direction;

                if (dir == SortDirection.Ascending)
                {
                    dir = SortDirection.Descending;
                }
                else
                {
                    dir = SortDirection.Ascending;
                }
            
                qs.Add("Direction", dir.ToString());
            }
            else
            {
                qs.Add("Direction", sort.Direction.ToString());
            }
        
            return qs.ToString();
        }
    }
}