public static void AddFormulaCacheElement(this IXmlSerializerRepository <SerializationContext> serializerRepository, XElement element, SerializationContext serializationContext)
        {
            var formulasSerializer  = serializerRepository.SerializerFor(serializationContext.Formulas);
            var formulaCacheElement = formulasSerializer.Serialize(serializationContext.Formulas, serializationContext);

            serializationContext.ClearFomulaCache();
            if (!formulaCacheElement.HasElements)
            {
                return;
            }

            //only one node and that node is the string map list
            if (formulaCacheElement.Descendants().Count() == 1 && formulaCacheElement.Element(Constants.Serialization.STRING_MAP_LIST) != null)
            {
                return;
            }

            element.AddElement(formulaCacheElement);
        }