An example of a SchemeHandlerFactory that throws a NRE in 49.0.1

CustomSchemeHandlerFactory.cs

using CefSharp;

namespace BirdJournal.Html.Windows
{
    public sealed class CustomSchemeHandlerFactory : ISchemeHandlerFactory
    {
        readonly NancyService m_nancyService;

        public CustomSchemeHandlerFactory(NancyService nancyService)
        {
            m_nancyService = nancyService;
        }

        public IResourceHandler Create(IBrowser browser, IFrame frame, string schemeName, IRequest request)
        {
            // Defer to CEF for external requests
            return request.Url.Contains("localhost") ? new CustomSchemeHandler(m_nancyService) : null;
        }
    }
}