[Bug]: Application crash on deselection of `col_by_var` in `tm_t_exposure` module

[kartikeyakirar]

What happened?

The application crashes when the col_by_var option is deselected in the tm_t_exposure module. It appears that there is no validation check to handle the scenario when no variable is selected, which leads to an application failure.

sample app:

library(dplyr)

data <- teal_data()
data <- within(data, {
  ADSL <- tmc_ex_adsl
  ADEX <- tmc_ex_adex

  set.seed(1, kind = "Mersenne-Twister")
  labels <- col_labels(ADEX, fill = FALSE)
  ADEX <- ADEX %>%
    distinct(USUBJID, .keep_all = TRUE) %>%
    mutate(
      PARAMCD = "TDURD",
      PARAM = "Overall duration (days)",
      AVAL = sample(x = seq(1, 200), size = n(), replace = TRUE),
      AVALU = "Days"
    ) %>%
    bind_rows(ADEX)
  col_labels(ADEX) <- labels
})

datanames <- c("ADSL", "ADEX")
datanames(data) <- datanames
join_keys(data) <- default_cdisc_join_keys[datanames]

app <- init(
  data = data,
  modules = modules(
    tm_t_exposure(
      label = "Duration of Exposure Table",
      dataname = "ADEX",
      paramcd = choices_selected(
        choices = value_choices(data[["ADEX"]], "PARAMCD", "PARAM"),
        selected = "TDURD"
      ),
      col_by_var = choices_selected(
        choices = variable_choices(data[["ADEX"]], subset = c("SEX", "ARM")),
        selected = "SEX"
      ),
      row_by_var = choices_selected(
        choices = variable_choices(data[["ADEX"]], subset = c("RACE", "REGION1", "STRATA1", "SEX")),
        selected = "RACE"
      ),
      parcat = choices_selected(
        choices = value_choices(data[["ADEX"]], "PARCAT2"),
        selected = "Drug A"
      ),
      add_total = FALSE
    )
  ),
  filter = teal_slices(teal_slice("ADSL", "SAFFL", selected = "Y"))
)
if (interactive()) {
  shinyApp(app$ui, app$server)
}

sessionInfo()

No response

Relevant log output

No response

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