public ExcelExternalFiles(ExcelPackage package, XmlNamespaceManager namespaceManager) : base(namespaceManager)
        {
            BaseDirectory   = package.File?.DirectoryName;
            ExternalFileUri = new Dictionary <int, Uri>();
            Uri externalLinkUri = new Uri($"xl/externalLinks/externalLink1.xml", UriKind.Relative);
            var i = 1;

            while (package.Package.PartExists(externalLinkUri))
            {
                XmlDocument    externalLinkXml = new XmlDocument();
                ZipPackagePart zipPackagePart  = package.Package.GetPart(externalLinkUri);
                LoadXmlSafe(externalLinkXml, zipPackagePart.GetStream());

                TopNode = externalLinkXml.DocumentElement;
                string rId = GetXmlNodeString("/d:externalLink/d:externalBook/@r:id");
                if (zipPackagePart.TryGetRelationshipById(rId, out var relation))
                {
                    ExternalFileUri.Add(i, relation.TargetUri);
                }

                i++;
                externalLinkUri = new Uri($"xl/externalLinks/externalLink{i}.xml", UriKind.Relative);
            }
        }