DocFx is not building pdf in azure server agent

[gitsourabhmishranotes]

Error happen when converting pdf/toc.json to Pdf. Details: System.NullReferenceException: Object reference not set to an instance of an object. at UglyToad.PdfPig.Writer.PdfDocumentBuilder.CompleteDocument() at UglyToad.PdfPig.Writer.PdfDocumentBuilder.Dispose() at Microsoft.DocAsCode.HtmlToPdf.HtmlToPdfConverter.WriteOutlines(MemoryStream input, Stream output) in //src/Microsoft.DocAsCode.HtmlToPdf/HtmlToPdfConverter.cs:line 301 at Microsoft.DocAsCode.HtmlToPdf.HtmlToPdfConverter.SaveCore(Stream stream) in //src/Microsoft.DocAsCode.HtmlToPdf/HtmlToPdfConverter.cs:line 267 at Microsoft.DocAsCode.HtmlToPdf.HtmlToPdfConverter.Save(String outputFileName) in //src/Microsoft.DocAsCode.HtmlToPdf/HtmlToPdfConverter.cs:line 91 at Microsoft.DocAsCode.HtmlToPdf.ConvertWrapper.ConvertCore(String basePath, String pdfFileName, IList`1 htmlModels) in //src/Microsoft.DocAsCode.HtmlToPdf/ConvertWrapper.cs:line 342 at Microsoft.DocAsCode.HtmlToPdf.ConvertWrapper.<>c__DisplayClass7_0.b_1(ManifestItem tocFile) in //src/Microsoft.DocAsCode.HtmlToPdf/ConvertWrapper.cs:line 166

[yufeih]

Seems like a dup of #8987