protected IEnumerable <Uri> GetTransformedUrls() { return(_urls.Cast <string>().Select(s => { var url = s; if (string.IsNullOrEmpty(url)) { return null; } if (url.Contains("$(")) { url = GlobalVariables.Aggregate(url, (current, variable) => current.Replace("$(" + variable.Key + ")", variable.Value)); } if (!url.StartsWith("http://") && !url.StartsWith("https://")) { url = "http://" + url; } if (Uri.IsWellFormedUriString(url, UriKind.Absolute)) { return new Uri(url, UriKind.Absolute); } if (Uri.IsWellFormedUriString(url, UriKind.Relative)) { return new Uri(url, UriKind.Relative); } return null; }).Where(s => s != null)); }