public static void Insert(this X509ExtensionCollection exts, Int32 index, X509Extension extension) { if (extension == null) { throw new ArgumentNullException(nameof(extension)); } if (exts == null) { return; } if (index < 0 || index >= exts.Count) { throw new OverflowException(); } List <X509Extension> e = new List <X509Extension>(exts.Cast <X509Extension>()); e.Insert(index, extension); exts = new X509ExtensionCollection(); exts.AddRange(e); }