I am using bookdown for my project and I want the output files in the root directory. I read that I can set output_dir: "." to achieve this. I compiled the book with bookdown::render_book("index.Rmd", output_dir=".") and it worked until R returned the following error messege:
Error in dir.exists(x) : invalid filename argument

I prepared a minimal working example to reproduce the error (index.Rmd):

---
title: "title"
author: "author"
site: bookdown::bookdown_site
output:
  bookdown::pdf_book:
    toc: yes
---

# Acknowledgement{-}

Also posted this issue on Stackoverflow

Sessioninfo:

R version 3.6.2 (2019-12-12)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 18363), RStudio 1.2.5033

Locale:
  LC_COLLATE=German_Germany.1252 
  LC_CTYPE=German_Germany.1252   
  LC_MONETARY=German_Germany.1252
  LC_NUMERIC=C                   
  LC_TIME=German_Germany.1252    

Package version:
  base64enc_0.1.3 bookdown_0.17.2 digest_0.6.23  
  evaluate_0.14   glue_1.3.1      graphics_3.6.2 
  grDevices_3.6.2 highr_0.8       htmltools_0.4.0
  jsonlite_1.6.1  knitr_1.27      magrittr_1.5   
  markdown_1.1    methods_3.6.2   mime_0.9       
  Rcpp_1.0.3      rlang_0.4.4     rmarkdown_2.1  
  stats_3.6.2     stringi_1.4.5   stringr_1.4.0  
  tinytex_0.19    tools_3.6.2     utils_3.6.2    
  xfun_0.12       yaml_2.2.1     

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