var xmlParts = binding.CustomXMLParts
                .SelectByNamespace(NamespaceURI)
                .OfType<Office.CustomXMLPart>();

            int itemsCount = xmlParts.Count();

            var xml = xmlParts
                .DefaultIfEmpty(binding.CustomXMLParts.Add(serializer.Serialize(new WordDocument()), Type.Missing))
                .First().XML;

            return serializer.Deserialize(xml);

            var xml = (xmlParts.FirstOrDefault()
                ?? binding.CustomXMLParts.Add(serializer.Serialize(new WordRpsDocument()), Type.Missing))
                .XML;