Warning in Rmarkdown ( Warning in file(con, "r") : file("") only supports open = "w+" and open = "w+b": using the former)

Hi all,

would someone highlight what may be causing this warning in a flexdashboard with runtime:shiny set?

Warning in file(con, "r") :
  file("") only supports open = "w+" and open = "w+b": using the former

I'm suspecting it also affecting my backgroud color of the dashboard, which I cannot get it to be set to the colour I supply throughbslib