Bug of `prepare_ae_forestly`

[LittleBeannie]

adsl <- forestly_adsl
adae <- forestly_adae
adsl$TRTA <- factor(adsl$TRTA, levels = c("Placebo", "Xanomeline Low Dose"))
adae$TRTA <- factor(adae$TRTA, levels = c("Placebo", "Xanomeline Low Dose"))


meta <- meta_adam(population = adsl, observation = adae) |>
  define_plan(plan = plan(analysis = "ae_forest_plot",
                          population = "apat",
                          observation = "apat",
                          parameter = "any-AE"           
  )) |>
  # ----------------------------------------- #
  # define populations
  # ----------------------------------------- #
  define_population(name = "apat",
                    group = "TRTA",
                    subset = SAFFL == "Y" ,
                    label = "All Participants as Treated Population",
                    var = c("USUBJID", "TRTA", "RACE", "SEX", "AGE", "AGEU")) |>
  # ----------------------------------------- #
  # define observations
  # ----------------------------------------- #
  define_observation(name = "apat",
                     group = "TRTA",
                     subset = SAFFL == "Y" ,
                     label = "All Participants as Treated Population") |>
  # ----------------------------------------- #
  # define analysis like 1 row in A&R grid
  # ----------------------------------------- #
  define_analysis(name = "ae_forest_plot",
                  label = "Interactive AE Forest Plot") |>
  # ----------------------------------------- #
  # parameters for AE analysis    
  # ----------------------------------------- #
  # Any AEs
  define_parameter(name = "any-AE",
                   subset = SAFFL == "Y",
                   label = "Any AEs",
                   var = "AEDECOD", soc = "AEBODSYS", term1 = "", term2 = "") |>
  meta_build()

meta |> prepare_ae_forestly(population = "apat", observation = "apat", ae_listing_display = c("USUBJID", "RACE", "SEX", "AEG", "AEGU"))

The root cause is that, "AGEU" is a variable in adsl, while it doesn't exist in adae.

After fixing the bug, please also improve the following:

• The default of var = ... in define_population should be NULL, where users MUST provides a list of variables
• The default of var = ... in define_observation should be NULL, where users MUST provides a list of variables