I am trying to implement UmbracoHttpHandler with the code below. The handler is linked up in the media folder's web.config. Everything works fine when the class inherits from IHttpHandler, but when I switch it to inherit from UmbracoHttpHandler as shown below, I start getting Object reference not set to an instance of an object. immediately upon trying to load any media, before it hits any breakpoints in MediaHttpHandler.cs.

Any ideas what I am doing wrong?

public class MediaHttpHandler : UmbracoHttpHandler
{
    public override bool IsReusable => true;

    public override void ProcessRequest(HttpContext context)
    {
        string requestedFile = context.Server.MapPath(context.Request.FilePath);

        switch (Path.GetExtension(requestedFile))
        {
            case ".jpg":
                context.Response.ContentType = "image/jpg";
                break;

            // Etc... several more of these.

            default:
                context.Response.ContentType = "text/plain";
                break;
        }

        if (requestedFile != null)
        {
            context.Response.TransmitFile(requestedFile);
            context.Response.End();
        }
        else
        {
            context.Response.StatusCode = 404;
        }
    }
}