work around the empty bibliography in the BETS package: nmecsys/BETS#18

DESCRIPTION

@@ -1,7 +1,7 @@
 Package: rmarkdown
 Type: Package
 Title: Dynamic Documents for R
-Version: 2.5.3
+Version: 2.5.4
 Authors@R: c(
   person("JJ", "Allaire", role = "aut", email = "[email protected]"),
   person("Yihui", "Xie", role = c("aut", "cre"), email = "[email protected]", comment = c(ORCID = "0000-0003-0645-5666")),

R/output_format.R

@@ -774,6 +774,8 @@ is_pandoc_to_html <- function(options) {
 
 citeproc_required <- function(yaml_front_matter,
                               input_lines = NULL) {
+  # TODO: remove the hack below after BETS is updated on CRAN https://github.com/nmecsys/BETS/pull/18
+  if (tryCatch(xfun::check_old_package('BETS', '0.4.9'), error = function(e) FALSE)) return(FALSE)
   (
     is.null(yaml_front_matter$citeproc) ||
       yaml_front_matter$citeproc