[BUG] Beamer export fails with async export [9.5.3 (9.5.3-g4197fc @ /home/thomas/.emacs.d/straight/build/org/)]

[Thomas Freeman <tlfree87@gmail.com>]

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

When exporting a LaTeX beamer presentation as an asynchronous process
(by using C-a prior to selecting the export option), the export fails with the following error:

(error "Unknown \"nil\" back-end: Aborting export")

This does not occur when exporting the same buffer to HTML or to
standard LaTeX. What should happen is that the export occurs in the
background just as it would when run in the foreground. This is
especially frustrating if org-export-in-background is set to t by
default.

Details of my setup are below:

Emacs  : GNU Emacs 28.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.30, cairo version 1.16.0)
Package: Org mode version 9.5.3 (9.5.3-g4197fc @ /home/thomas/.emacs.d/straight/build/org/)

current state:
==============
(setq
 org-link-elisp-confirm-function 'yes-or-no-p
 org-directory "~/Dropbox/gtd"
 org-cite-insert-processor 'citar
 org-hide-emphasis-markers t
 org-bibtex-headline-format-function #[257 "\300\236A\207" [:title] 3 "\n\n(fn ENTRY)"]
 org-log-into-drawer t
 org-agenda-files '("~/Dropbox/gtd")
 org-persist-after-read-hook '(org-element--cache-persist-after-read)
 org-refile-targets '((org-agenda-files :maxlevel . 3))
 org-export-before-parsing-hook '(org-attach-expand-links)
 org-cycle-tab-first-hook '(org-babel-hide-result-toggle-maybe
                            org-babel-header-arg-expand)
 org-default-notes-file "~/Dropbox/gtd/inbox.org"
 org-refile-use-outline-path 'file
 org-publish-timestamp-directory "/home/thomas/.emacs.d/var/org/timestamps/"
 org-archive-hook '(org-attach-archive-delete-maybe)
 org-cite-follow-processor 'citar
 org-odt-format-inlinetask-function 'org-odt-format-inlinetask-default-function
 org-ascii-format-drawer-function #[771 "\207" [] 4 "\n\n(fn NAME CONTENTS WIDTH)"]
 org-cycle-hook '(org-cycle-hide-archived-subtrees org-cycle-show-empty-lines
                  org-cycle-optimize-window-after-visibility-change)
 org-persist-before-read-hook '(org-element--cache-persist-before-read)
 org-font-lock-set-keywords-hook '(doom-themes-enable-org-fontification)
 org-modules '(ol-bbdb ol-bibtex ol-docview ol-doi org-habit)
 org-mode-hook '(#[0 "\301\211\207"
                   [imenu-create-index-function org-imenu-get-tree] 2]
                 org-superstar-mode visual-line-mode turn-on-flyspell
                 #[0 "\300\301\302\303\304$\207"
                   [add-hook change-major-mode-hook org-fold-show-all append
                    local]
                   5]
                 #[0 "\300\301\302\303\304$\207"
                   [add-hook change-major-mode-hook org-babel-show-result-all
                    append local]
                   5]
                 org-babel-result-hide-spec org-babel-hide-all-hashes
                 olivetti-mode mixed-pitch-mode org-eldoc-load)
 org-babel-load-languages '((awk . t) (calc . t) (css . t) (emacs-lisp . t)
                            (eshell . t) (gnuplot . t) (dot . t) (latex . t)
                            (ledger . t) (octave . t) (plantuml . t) (R . t)
                            (sed . t) (shell . t))
 org-id-locations-file "/home/thomas/.emacs.d/var/org/id-locations.el"
 org-latex-format-drawer-function #[514 "\207" [] 3 "\n\n(fn _ CONTENTS)"]
 org-latex-format-headline-function 'org-latex-format-headline-default-function
 org-confirm-shell-link-function 'yes-or-no-p
 org-html-format-drawer-function #[514 "\207" [] 3 "\n\n(fn NAME CONTENTS)"]
 outline-isearch-open-invisible-function 'outline-isearch-open-invisible
 org-stuck-projects '("+project/-MAYBE-DONE" ("NEXT" "TODO") nil "\\<IGNORE\\>")
 org-startup-indented t
 org-latex-classes '(("beamer" "\\documentclass[presentation]{beamer}"
                      ("\\section{%s}" . "\\section*{%s}")
                      ("\\subsection{%s}" . "\\subsection*{%s}")
                      ("\\subsubsection{%s}" . "\\subsubsection*{%s}"))
                     ("article" "\\documentclass[11pt]{article}"
                      ("\\section{%s}" . "\\section*{%s}")
                      ("\\subsection{%s}" . "\\subsection*{%s}")
                      ("\\subsubsection{%s}" . "\\subsubsection*{%s}")
                      ("\\paragraph{%s}" . "\\paragraph*{%s}")
                      ("\\subparagraph{%s}" . "\\subparagraph*{%s}"))
                     ("report" "\\documentclass[11pt]{report}"
                      ("\\part{%s}" . "\\part*{%s}")
                      ("\\chapter{%s}" . "\\chapter*{%s}")
                      ("\\section{%s}" . "\\section*{%s}")
                      ("\\subsection{%s}" . "\\subsection*{%s}")
                      ("\\subsubsection{%s}" . "\\subsubsection*{%s}"))
                     ("book" "\\documentclass[11pt]{book}"
                      ("\\part{%s}" . "\\part*{%s}")
                      ("\\chapter{%s}" . "\\chapter*{%s}")
                      ("\\section{%s}" . "\\section*{%s}")
                      ("\\subsection{%s}" . "\\subsection*{%s}")
                      ("\\subsubsection{%s}" . "\\subsubsection*{%s}"))
                     )
 org-plantuml-jar-path "/home/thomas/.emacs.d/plantuml/plantuml.jar"
 org-odt-format-headline-function 'org-odt-format-headline-default-function
 org-export-in-background t
 org-agenda-before-write-hook '(org-agenda-add-entry-text)
 org-babel-tangle-lang-exts '(("sed" . "sed") ("latex" . "tex") ("awk" . "awk")
                              ("emacs-lisp" . "el") ("elisp" . "el"))
 org-src-mode-hook '(org-src-babel-configure-edit-buffer
                     org-src-mode-configure-edit-buffer
                     doom-modeline-set-org-src-modeline)
 org-confirm-elisp-link-function 'yes-or-no-p
 org-tags-exclude-from-inheritance '("project")
 org-cite-activate-processor 'citar
 org-todo-keywords '((sequence "TODO(t)" "WAITING(w)" "|" "DONE(d)" "CANCELED(c)")
                     )
 org-speed-command-hook '(org-speed-command-activate
                          org-babel-speed-command-activate)
 org-html-format-inlinetask-function 'org-html-format-inlinetask-default-function
 org-clock-persist-file "/home/thomas/.emacs.d/var/org/clock-persist.el"
 org-ascii-format-inlinetask-function 'org-ascii-format-inlinetask-default
 org-odt-format-drawer-function #[514 "\207" [] 3 "\n\n(fn NAME CONTENTS)"]
 org-persist-directory "/home/thomas/.emacs.d/var/org/persist/"
 org-fold-core-isearch-open-function 'org-fold--isearch-reveal
 org-latex-format-inlinetask-function 'org-latex-format-inlinetask-default-function
 org-persist-before-write-hook '(org-element--cache-persist-before-write)
 org-tab-first-hook '(org-babel-hide-result-toggle-maybe
                      org-babel-header-arg-expand)
 org-link-shell-confirm-function 'yes-or-no-p
 org-babel-pre-tangle-hook '(save-buffer)
 org-agenda-loop-over-headlines-in-active-region nil
 org-agenda-start-on-weekday nil
 org-todo-keyword-faces '(("TODO" . org-warning) ("WAITING" . "yellow")
                          ("CANCELED" :foreground "blue" :weight bold)
                          ("DONE" . org-done))
 org-cite-global-bibliography '("~/bib/bib.bib")
 org-occur-hook '(org-first-headline-recenter)
 org-metadown-hook '(org-babel-pop-to-session-maybe)
 org-link-parameters '(("attachment" :follow org-attach-follow :complete
                        org-attach-complete-link)
                       ("doi" :follow org-link-doi-open :export
                        org-link-doi-export)
                       ("docview" :follow org-docview-open :export
                        org-docview-export :store org-docview-store-link)
                       ("bibtex" :follow org-bibtex-open :store
                        org-bibtex-store-link)
                       ("bbdb" :follow org-bbdb-open :export org-bbdb-export
                        :complete org-bbdb-complete-link :store
                        org-bbdb-store-link)
                       ("id" :follow org-id-open) ("file+sys") ("file+emacs")
                       ("shell" :follow org-link--open-shell)
                       ("news" :follow
                        #[514 "\301\300\302Q\"\207" ["news" browse-url ":"] 6
                          "\n\n(fn URL ARG)"]
                        )
                       ("mailto" :follow
                        #[514 "\301\300\302Q\"\207" ["mailto" browse-url ":"]
                          6 "\n\n(fn URL ARG)"]
                        )
                       ("https" :follow
                        #[514 "\301\300\302Q\"\207" ["https" browse-url ":"]
                          6 "\n\n(fn URL ARG)"]
                        )
                       ("http" :follow
                        #[514 "\301\300\302Q\"\207" ["http" browse-url ":"] 6
                          "\n\n(fn URL ARG)"]
                        )
                       ("ftp" :follow
                        #[514 "\301\300\302Q\"\207" ["ftp" browse-url ":"] 6
                          "\n\n(fn URL ARG)"]
                        )
                       ("help" :follow org-link--open-help :store
                        org-link--store-help)
                       ("file" :complete org-link-complete-file)
                       ("elisp" :follow org-link--open-elisp))
 org-html-format-headline-function 'org-html-format-headline-default-function
 org-metaup-hook '(org-babel-load-in-session-maybe)
 org-refile-allow-creating-parent-nodes 'confirm
 org-latex-pdf-process '("pdflatex -interaction nonstopmode -output-directory %o %f" "biber %b" "pdflatex -interaction nonstopmode -output-directory %o %f" "pdflatex -interaction nonstopmode -output-directory %o %f")
 org-outline-path-complete-in-steps nil
 org-tags-column 0
 org-src-lang-modes '(("redis" . redis) ("php" . php) ("arduino" . arduino)
                      ("plantuml" . plantuml) ("C" . c) ("C++" . c++)
                      ("asymptote" . asy) ("bash" . sh) ("beamer" . latex)
                      ("calc" . fundamental) ("cpp" . c++) ("ditaa" . artist)
                      ("desktop" . conf-desktop) ("dot" . fundamental)
                      ("elisp" . emacs-lisp) ("ocaml" . tuareg)
                      ("screen" . shell-script) ("shell" . sh) ("sqlite" . sql)
                      ("toml" . conf-toml))
 org-superstar-item-bullet-alist '((42 . 8226) (43 . 10148) (45 . 8226))
 )

Thanks for all you do,

Thomas