public IActionResult Details(string id)
{
  if (string.IsNullOrWhiteSpace(id))
    return RedirectToAction("index", "home");

  var selectedCfp = _cfpContext.Cfps.SingleOrDefault(cfp => cfp.Slug == id);

  if (selectedCfp == null)
  {
    // Check it the id happens to be a Guid
    if (Guid.TryParse(id, out Guid guidId))
    {
      if (guidId != Guid.Empty)
        selectedCfp = _cfpContext.Cfps.SingleOrDefault(cfp => cfp.Id == guidId);
    }

    if (selectedCfp == null)
      // TODO to error page?
      return RedirectToAction("index", "home");
  }

  // ... Non relevant code

  return View(selectedCfp);
}