ASP.NET WebAPI routing confusing me with null paramters - asp.net-web-api

Question

I can't figure out why I need to create an empty method signature to allow a Get rest call with 3 null parameters to work. I have the following Code:
public class SessionPresenterController : ApiController
{
public HttpResponseMessage Get()
{
return Get(null, null, null);
}
public HttpResponseMessage Get(int? codeCampYearId, int? sessionId, int? attendeesId)
{
and in my WebApiConfig I have
config.Routes.MapHttpRoute
("API Default Rest", "rest/{controller}/{id}",
new { id = RouteParameter.Optional });
config.Routes.MapHttpRoute
("API Default RPC", "rpc/{controller}/{action}/{id}",
new { id = RouteParameter.Optional });
If I call /rest/SessionPresenter without any parameters and I Don't have the Get() defined, the Get with the three null parameters is not found.
Why not?

Answer 1

Try specifying defaults for your parameters:
public HttpResponseMessage Get(
int? codeCampYearId = null,
int? sessionId = null,
int? attendeesId = null)
{
//...
}

Answer 2

Jacobs' snippet will solve your issue. Let's answert the question why not? why get is not found..
There is a complete documentation of the Routing and Action Selection. Let's use some extratc and reveal what happens:
Action Selection
Create a list of all actions on the controller that match the HTTP request method.
If the route dictionary has an "action" entry, remove actions whose name does not match this value.
Try to match action parameters to the URI, as follows:
For each action, get a list of the parameters that are a simple type, where the binding gets the parameter from the URI. Exclude optional parameters.
From this list, try to find a match for each parameter name, either in the route dictionary or in the URI query string. Matches are case insensitive and do not depend on the parameter order.
Select an action where every parameter in the list has a match in the URI.
If more that one action meets these criteria, pick the one with the most parameter matches.
Other words, if there will be only Get with three parameters (omited Get()), to decided which action should be selected:
Selected was Get(int? codeCampYearId, int? sessionId, int? attendeesId)
still the Get(int? codeCampYearId, int? sessionId, int? attendeesId) is selected
URL is /rest/SessionPresenter
no optional parameters excluded. All have to be found
URL does not have a match for all three parameters
So to solve it, we have to either pass all params (empty, null):
/rest/SessionPresenter?codeCampYearId&attendeesId&sessionid
Or change the signature to have parameters optinal (Jacobs' answer), and skipped during the action selection