Hi folks, how do you find image url?

I have tried drilling down into the properties, I receive a null reference at the following code Udi tempImageUrl = mediaItem.Url;

Full code below

 public ActionResult RenderFeatured()
    {
        List<FeaturedItem> model = new List<FeaturedItem>();
        IPublishedContent homePage = CurrentPage.AncestorOrSelf(1).DescendantsOrSelf().Where(x => x.DocumentTypeAlias == "home").FirstOrDefault();
        ArchetypeModel featuredItems = homePage.GetPropertyValue<ArchetypeModel>("featuredItems");

        foreach (ArchetypeFieldsetModel fieldset in featuredItems)
        {
            Udi imageId = fieldset.GetValue<Udi>("image");
            var mediaItem = Umbraco.Media(imageId);

            Udi tempImageUrl = mediaItem.Url;
            string imageUrl = tempImageUrl.ToString();