Subfolders of reports folder without a report are attempted to be knitted anyway

Error in seinebasin2 which as a "images" subfolder in "reports" which obvisouly does not contain a report to knit:

Rendering book in directory 'C:/DocDD/Inrae/2018 Water JPI IN-WOT/2_Data/sources/seinebasin2/reports/images'
Erreur dans value[[3L]](cond) : 
Error on:
bookdown::render_book(
input = "C:/DocDD/Inrae/2018 Water JPI IN-WOT/2_Data/sources/seinebasin2/reports/images",
output_format = "bookdown::gitbook",
output_dir = "C:/DocDD/Inrae/2018 Water JPI IN-WOT/2_Data/sources/seinebasin2/public/reports/images")
No input R Markdown files found from the current directory C:/DocDD/Inrae/2018 Water JPI IN-WOT/2_Data/sources/seinebasin2/reports/images or in the rmd_files field of _bookdown.yml
Appels : tryCatch -> tryCatchList -> tryCatchOne -> <Anonymous>
Exécution arrêtée
Erreur dans render_report(input = file.path(reports_dir, report), output_dir = file.path(publish_dir,  : 
  render_report has raised an error (See message above)
De plus : Messages d'avis :
1: Dans FUN(X[[i]], ...) :
  File C:/DocDD/Inrae/2018 Water JPI IN-WOT/2_Data/sources/seinebasin2/reports/images/index.Rmd not found, the folder images is ignored