public static bool IsGUID(string expression)  {      if (expression != null)      {          Regex guidRegEx = new Regex(@"^(\{{0,1}([0-9a-fA-F]){8}-([0-9a-fA-F]){4}-([0-9a-fA-F]){4}-([0-9a-fA-F]){4}-([0-9a-fA-F]){12}\}{0,1})$");          return guidRegEx.IsMatch(expression);      }      return false;  }