Web Api 2: NotFound() with content?

Question

I have the following resource used to return specific company information:

[HttpGet]
[Route("{companyId:Guid}")]
public IHttpActionResult Get(Guid companyId)
{
    var company = CompanyRepository.Find(companyId);

    if (company == null)
    {
        return NotFound();
    }
    else
    {
        var responseModel = new CompanyResponseModel()
        {
            CompanyId = company.Id,
            Name = company.Name
        };

        return Ok(responseModel);
    }
}

Why can we not include content into the NotFound() call?

For example, I would like to include an error response model with a message "Company ID does not exist".

Is this perhaps against RESTful design?

Answer 1

According to RFC2616 Section 10 the 404 does not return any information about the resource itself. But if you want to use the 404 you can use this instead:

return Content(HttpStatusCode.NotFound, "Your Content/Message");