This is a patched version of NHibernate to prevent background JIT from failing.
Applied https://nhibernate.jira.com/browse/NH-2958:

        private static XmlSerializer _mappingDocumentSerializer = null; 

        private XmlSerializer mappingDocumentSerializer 
        { 
            get 
            { 
                if (_mappingDocumentSerializer == null) 
                    _mappingDocumentSerializer = new XmlSerializer(typeof (HbmMapping)); 
                return _mappingDocumentSerializer; 
            } 
        }