LastChanceContentFinder (404 not found for umbraco)

MyApplicationEvents.cs

 public class MyApplicationEvents : ApplicationEventHandler
 {
    protected override void ApplicationStarting(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
    {
        ContentLastChanceFinderResolver.Current.SetFinder(new MyLastChanceContentFinder());
    }
 }

MyLastChanceContentFinder.cs

using umbraco.cms.businesslogic.web;
using Umbraco.Web;
using Umbraco.Web.Routing;


    /// <summary>
    /// Acts as the 404 content finder for the  website. If the requester url fails all other default Umbraco content finders, this one kicks in.
    /// It must be registered in the application events with ContentLastChanceFinderResolver.Current.SetFinder(new MyLastChangeContentFinder());
    /// Because this is the last chance content finder, it will ALWAYS return a 404. 
    /// </summary>
    public sealed class MyLastChanceContentFinder : IContentFinder
    {
        public bool TryFindContent(PublishedContentRequest contentRequest)
        {
            if (!contentRequest.HasDomain)
                return false;
            var contentCache = contentRequest.RoutingContext.UmbracoContext.ContentCache;
            int? rootContentId = contentRequest.UmbracoDomain.RootContentId;
            if (rootContentId == null)
            {
                return false;
            }
            var domainRoot = contentCache.GetById(rootContentId.Value);
            var segments = contentRequest.Uri.AbsolutePath.Split(new[] { '/' }, StringSplitOptions.RemoveEmptyEntries);
            if (!segments.Any())
            {
                return false;
            }
            var firstSegment = segments.FirstOrDefault();
            var root = domainRoot.Children.FirstOrDefault(x => x.UrlName == firstSegment);
            root = root ?? domainRoot.Children.First();
            var page = root.Descendants().FirstOrDefault(x => x.DocumentTypeAlias == My.Constants.DocumentTypes.NotFound.Alias );
            if (page == null) return false;

            contentRequest.PublishedContent = page;
            return true;
        }
    }