Need help understanding why the partial view error exists in custom route

Questions
1

note: I’m using a theme I bought from uskinned.

when I navigate to a page (“pageA”)(id: 1183) with document type DocTypeA that has the following template:

@inherits Umbraco.Web.Mvc.UmbracoTemplatePage
@{
Layout = “master.cshtml”;
}
.
.
.

and master.cshtml is
@inherits Umbraco.Web.Mvc.UmbracoTemplatePage
@{
Layout = null;
}
.
.
@Html.Partial(“section/SEOPageHead”, @Model.Content) ← Line B
.
.

and SEOPageHead.cshtml is
@inherits Umbraco.Web.Mvc.UmbracoTemplatePage
@{
IPublishedContent homeNode = Model.Content.AncestorOrSelf(1); ← Line C
.
.

there are no errors.

If I hover over Model in line B or C above in debug mode, I see both Model.Content and Model.CurrentCulture.

I then followed Custom MVC routing in Umbraco - Shazwazza
to implement the following custom route
localhost/cars/views/3

using the class..

public class CarChartsController : Umbraco.Web.Mvc.PluginController
{

    public CarChartsController ()
        : this(UmbracoContext.Current)
    {
    }

    public CarChartsController (UmbracoContext umbracoContext)
        : base(umbracoContext)
    {
    }

    public ActionResult Views(string id)
    {

        var y = umbracoContext.ContentCache.GetById(1183); //this is the same doc id as pageA/DocTypeA from the very top
        return View("~/Views/views.cshtml", CreateRenderModel(y));
    }
    
    private RenderModel CreateRenderModel(IPublishedContent content)
    {
        var model = new RenderModel(content, CultureInfo.CurrentUICulture);

        //add an umbraco data token so the umbraco view engine executes
        RouteData.DataTokens["umbraco"] = model;
        //new UmbracoHelper()
        return model;
    }

}

views.cshtml is

@inherits Umbraco.Web.Mvc.UmbracoTemplatePage
@{
Layout = “USNMaster.cshtml”;

}
.
.
.

now if navigate to localhost/cars/views/3, I get a system.nullreferenceexception error during debug.

now if I change Line B to
@Html.Partial(“section/SEOPageHead”, @Model) // @Model.Content replaced by @Model

everything works when I navigate to the custom route localhost/cars/views/3.

Any ideas why the partial view when going via custrom route didn’t work originally but did work when going through the normal umbraco route?

This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/75619-need-help-understanding-why-the-partial-view-error-exists-in-custom-route