Updating error message in rename_ard_columns() (#341)

**What changes are proposed in this pull request?**
Error message update for `rename_ard_columns(unlist)` to indicate the
function to call to assist with NULL values.

<img width="978" alt="image"
src="https://github.com/user-attachments/assets/2fa0d2f6-be50-4223-8c86-78bfa3eae226">


**Reference GitHub issue associated with pull request.** _e.g., 'closes
#<issue number>'_
closes #332


--------------------------------------------------------------------------------

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R/replace_null_statistic.R

@@ -1,6 +1,6 @@
 #' Replace NULL Statistics with Specified Value
 #'
-#' When a statistical summary function errors, the `"statistic"` column will be
+#' When a statistical summary function errors, the `"stat"` column will be
 #' `NULL`. It is, however, sometimes useful to replace these values with a
 #' non-`NULL` value, e.g. `NA`.
 #'

R/shift_ard_columns.R

@@ -52,7 +52,8 @@ rename_ard_columns <- function(x, columns = c(all_ard_groups(), all_ard_variable
       if (length(unlisted) != length(x[[unlist_var]])) {
         cli::cli_abort(
           c("Cannot unlist column {.val {unlist_var}}. The unlisted result is not the same length as the original.",
-            "i" = "This often occurs when the column contains {.code NULL} values."
+            "i" = "This often occurs when the column contains {.code NULL} values.",
+            if (unlist_var == "stat") c("*" = "Run {.fun cards::replace_null_statistic} to replace {.code NULL} values with {.val {NA}}.") # styler: off
           ),
           call = get_cli_abort_call()
         )

tests/testthat/_snaps/rename_ard_columns.md

@@ -44,4 +44,5 @@
       Error in `rename_ard_columns()`:
       ! Cannot unlist column "stat". The unlisted result is not the same length as the original.
       i This often occurs when the column contains `NULL` values.
+      * Run `cards::replace_null_statistic()` to replace `NULL` values with NA.