Hierarchical select in module, error unclear

Hi, I am working on a shiny project with modules (golem framework), and I tried implementing the example here:

I can get that working no problem as a single file. I'm a little out of my depth here, but here's how I make that into a module:

#' temp_bar_plot UI Function
#'
#' @description A shiny Module.
#'
#' @param id,input,output,session Internal parameters for {shiny}.
#'
#' @noRd 
#'
#' @importFrom shiny NS tagList 
#' 
mod_temp_bar_plot_ui <- function(id){
  ns <- NS(id)
  tagList(
    fluidPage(
      selectInput("territory", "Territory", choices = unique(sales$TERRITORY)), selected = "NA",
      selectInput("customername", "Customer", choices = NULL),
      selectInput("ordernumber", "Order number", choices = NULL),
      tableOutput("data")
    )
  )
}
    
#' temp_bar_plot Server Functions
#'
#' @noRd 
mod_temp_bar_plot_server <- function(id){
  moduleServer( id, function(input, output, session){
    ns <- session$ns
    territory <- reactive({
      filter(sales, TERRITORY == input$territory)
    })
    observeEvent(territory(), {
      choices <- unique(territory()$CUSTOMERNAME)
      updateSelectInput(inputId = "customername", choices = choices) 
    })
    
    customer <- reactive({
      req(input$customername)
      filter(territory(), CUSTOMERNAME == input$customername)
    })
    observeEvent(customer(), {
      choices <- unique(customer()$ORDERNUMBER)
      updateSelectInput(inputId = "ordernumber", choices = choices)
    })
    
    output$data <- renderTable({
      req(input$ordernumber)
      customer() %>% 
        filter(ORDERNUMBER == input$ordernumber) %>% 
        select(QUANTITYORDERED, PRICEEACH, PRODUCTCODE)
    })
  })
}
    
## To be copied in the UI
# mod_temp_bar_plot_ui("temp_bar_plot_ui_1")
    
## To be copied in the server
# mod_temp_bar_plot_server("temp_bar_plot_ui_1")

sales is loaded at runtime. I get this error:

Warning: Error in : Problem with `filter()` input `..1`.
ℹ Input `..1` is `TERRITORY == input$territory`.
x Input `..1` must be of size 2823 or 1, not size 0.
  [No stack trace available]

It doesn't like the first call of the first reactive in the observeEvent. I thought the Hadley's discussion of freezing reactive inputs might help, but no luck. This would be a great workflow if I could get it to work!

Thanks for all the help!

I believe I was able to reproduce your error without involving shiny

filter(iris,
       Species == NULL)
Error: Problem with `filter()` input `..1`.
i Input `..1` is `Species == NULL`.
x Input `..1` must be of size 150 or 1, not size 0.

I would recommend you should look to use shiny features like req() or validate/need, or otherwise do some conditional logic to anticipate such cases.