Adding sitemap.xml custom route causes EnsureLoggedInForPreview.Process

Question

I am adding a sitemap to my site. I created a custom route and am adding it in a pipeline processor. When I brows to the page I get the following error:

Object reference not set to an instance of an object.

[NullReferenceException: Object reference not set to an instance of an object.]  
Sitecore.Mvc.Pipelines.Request.RequestBegin.EnsureLoggedInForPreview.Process( PipelineArgs args) +30
 (Object , Object[] ) +70
 Sitecore.Pipelines.CorePipeline.Run(PipelineArgs args) +468
 Sitecore.Pipelines.DefaultCorePipelineManager.Run(String pipelineName, PipelineArgs args, String pipelineDomain) +21
 Sitecore.Mvc.Pipelines.PipelineService.RunPipeline(String pipelineName, TArgs args) +194
 Sitecore.Mvc.Routing.RouteHttpHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData) +73  System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +1122
 System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step) +213
 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +131

Here is the pipeline:

public void Process(PipelineArgs args)
    {
        RouteTable.Routes.MapRoute("Sitemap", "sitemap.xml",
            new { controller = "XmlSitemap", action = "XmlSitemap" });

        });
    }

And I am patching it in as per Sitecore's documentation:

<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
  <sitecore>
    <pipelines>
      <initialize>
        <processor type="DD.Platform.Sc.Pipelines.Mvc.RouteConfig,DD.Platform.Sc"
               patch:after="processor[@type='Sitecore.Pipelines.Loader.EnsureAnonymousUsers, Sitecore.Kernel']" />
      </initialize>
    </pipelines>
  </sitecore>
</configuration>

Its definitely something about the .xml. If I make the custom route just 'sitemap' it works.

Answer 1

I had to explicitly allow xml files using the Sitecore FilterUrlExtensions setting:

<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
  <sitecore>
    <pipelines>
      <preprocessRequest>
        <processor type='Sitecore.Pipelines.PreprocessRequest.FilterUrlExtensions, Sitecore.Kernel'>
      <param desc="Allowed extensions (comma separated)">aspx, ashx, asmx, asp, xml</param>
        </processor>
      </preprocessRequest>
    </pipelines>
  </sitecore>
</configuration>