Progress bar properties cannot be cleared by setting `NULL`

Progress$set(value = NULL) should remove the progress bar but it does not.

message and detail can be hidden by setting "" or "NA" but the bar persists.

example app

``` library(shiny) ui <- fluidPage() srv <- function(input, output) { prog <- Progress$new() prog$set(message = "old message", value = 0) Sys.sleep(2) prog$set(message = "new message", value = 1) Sys.sleep(2) prog$set(message = NULL, value = NULL) Sys.sleep(2) prog$close() } shinyApp(ui, srv) ```

session info

``` R version 4.4.0 (2024-04-24 ucrt) Platform: x86_64-w64-mingw32/x64 Running under: Windows 10 x64 (build 19045) Matrix products: default locale: [1] LC_COLLATE=English_United States.utf8 [2] LC_CTYPE=English_United States.utf8 [3] LC_MONETARY=English_United States.utf8 [4] LC_NUMERIC=C [5] LC_TIME=English_United States.utf8 time zone: Europe/Warsaw tzcode source: internal attached base packages: [1] stats graphics grDevices utils datasets methods base other attached packages: [1] shiny_1.8.1.1 loaded via a namespace (and not attached): [1] digest_0.6.35 later_1.3.2 R6_2.5.1 httpuv_1.6.15 [5] fastmap_1.2.0 magrittr_2.0.3 cachem_1.1.0 memoise_2.0.1 [9] htmltools_0.5.8.1 lifecycle_1.0.4 promises_1.3.0 cli_3.6.2 [13] xtable_1.8-4 sass_0.4.9 jquerylib_0.1.4 compiler_4.4.0 [17] tools_4.4.0 bslib_0.7.0 mime_0.12 Rcpp_1.0.12 [21] rlang_1.1.3 jsonlite_1.8.8 ```

rstudio / shiny

Progress bar properties cannot be cleared by setting `NULL` #4070