controlleroption.cs

[Route("api/[controller]")]
public class CustomersController : Controller
{
    private readonly CustomerRepository _customerRepository;

    public CustomersController()
    {
        _customerRepository = new CustomerRepository();
    }

    // GET api/values/5
    [HttpGet("{id}")]
    public IActionResult Get(int id)
    {
        // Returns null if customer doesn't exist.
        var customer = _customerRepository.GetOptionById(id);

        return customer.Match<IActionResult>(
            some: value => new JsonResult(new
                    {
                        CustomerId = value.CustomerId,
                        Name = value.Name
                    }), 
            none: () => new StatusCodeResult(404));
    }
}