ActionUsingOptionTypes.cs

public HttpResponseMessage Get(int id)
{
  return CustomerRepository.GetBy(id)
           .Match(
             c  => Request.CreateResponse(
                     HttpStatusCode.Found,
                     c),
             () => Request.CreateErrorResponse(
                     HttpStatusCode.NotFound,
                     String.Format("There is no customer having the ID '{0}'", id)));
}