The code chunk just above section B. Be sure it is tested seems incomplete in both printed book and the online version.
Specifically (where the <<<<<< is) :
server <- function(
input,
output,
session
){
# We start by creating a new instance of th <<<<<<
r6 <- MyDataProcessing$new()
# Passing this object to the two server functions
mod_data_cleaning_server("data_cleaning_ui_1", r6)
mod_plotting_server("plotting_ui_1", r6)
}
...