REST out header param is expected from the server

[WebFreak001]

The documentation says that out REST headerParams are response headers that you don't send to the server, but if you don't send the header to the server it complains about a missing non-optional header parameter:

import vibe.d;

shared static this()
{
	auto settings = new HTTPServerSettings;
	settings.port = 3000;
	settings.bindAddresses = ["::1", "127.0.0.1"];
	auto router = new URLRouter;
	router.registerRestInterface(new Rest);
	listenHTTP(settings, router);
}

interface IRest
{
	@headerParam("a", "X-A-Header")
	int getFoo(out string a);
}

class Rest : IRest
{
	int getFoo(out string a)
	{
		a = "hi";
		return 0;
	}
}

Now open http://localhost:3000/foo and you would expect it to return 0 and send back the X-A-Header with hi as value, however it returns this:

400 - Bad Request

Missing non-optional header parameter 'X-A-Header'.

Internal error information:
vibe.http.common.HTTPStatusException@../../home/webfreak/.dub/packages/vibe-d-0.7.32/vibe-d/source/vibe/web/rest.d(1072): Missing non-optional header parameter 'X-A-Header'.
----------------
??:? pure @safe bool std.exception.enforce!(bool).enforce(bool, lazy object.Throwable) [0x217bfd4]
??:? bool vibe.http.common.enforceHTTP!(bool).enforceHTTP(bool, vibe.http.status.HTTPStatus, lazy immutable(char)[], immutable(char)[], int) [0x2188383]
??:? bool vibe.http.common.enforceBadRequest!(bool).enforceBadRequest(bool, lazy immutable(char)[], immutable(char)[], int) [0x218831c]
??:? void vibe.web.rest.jsonMethodHandler!(int app.IRest.getFoo(out immutable(char)[]), 0uL, app.Rest).jsonMethodHandler(app.Rest, ref vibe.web.internal.rest.common.RestInterface!(app.Rest).RestInterface).handler(vibe.http.server.HTTPServerRequest, vibe.http.server.HTTPServerResponse) [0x218569a]
??:? _D4vibe4http6router9URLRouter13handleRequestMFC4vibe4http6server17HTTPServerRequestC4vibe4http6server18HTTPServerResponseZ21__T9__lambda4TmTAAyaZ9__lambda4MFmMAAyaZb [0x222c8ce]
??:? const(bool function(immutable(char)[], scope bool delegate(ulong, scope immutable(char)[][]))) vibe.http.router.MatchTree!(vibe.http.router.Route).MatchTree.doMatch [0x222d6b5]
??:? bool vibe.http.router.MatchTree!(vibe.http.router.Route).MatchTree.match(immutable(char)[], scope bool delegate(ulong, scope immutable(char)[][])) [0x222cf07]
??:? void vibe.http.router.URLRouter.handleRequest(vibe.http.server.HTTPServerRequest, vibe.http.server.HTTPServerResponse) [0x222c56d]
??:? bool vibe.http.server.handleRequest(vibe.core.stream.Stream, vibe.core.net.TCPConnection, vibe.http.server.HTTPListenInfo, ref vibe.http.server.HTTPServerSettings, ref bool) [0x2269a60]
??:? void vibe.http.server.handleHTTPConnection(vibe.core.net.TCPConnection, vibe.http.server.HTTPListenInfo) [0x2267ffc]
??:? void vibe.http.server.listenHTTPPlain(vibe.http.server.HTTPServerSettings).doListen(vibe.http.server.HTTPListenInfo, bool, bool).__lambda4(vibe.core.net.TCPConnection) [0x226799c]
??:? void vibe.core.drivers.libevent2_tcp.ClientTask.execute() [0x231aa24]
??:? void vibe.core.core.makeTaskFuncInfo!(void delegate()).makeTaskFuncInfo(ref void delegate()).callDelegate(vibe.core.core.TaskFuncInfo*) [0x21d8a3f]
??:? void vibe.core.core.CoreTask.run() [0x22a5c76]
??:? void core.thread.Fiber.run() [0x23bbc9b]
??:? fiber_entryPoint [0x23bb9fe]
??:? [0xffffffff]