Hi all,
the unpatched version doesn’t work for me. I’ve reinstalled
AUCTeX (from Elpa) and restarted the computer to be sure that Emacs
picks up everything as updated. The only mention of xparse.el or .elc
in the Messages buffer is

    Loading ~/.emacs.d/elpa/auctex-13.0.15/style/xparse.elc...done

then, towards the end

    Sorting xparse-macro...done
    Removing duplicates...done
    replace-regexp-in-string: Wrong type argument: arrayp, nil

For the sake of completeness,

    find ~/.emacs.d/ -name 'xparse.el*'

returns

    ~/.emacs.d/elpa/auctex-13.0.15/style/xparse.el
    ~/.emacs.d/elpa/auctex-13.0.15/style/xparse.elc

Could it be because I’m still running TeX Live 2019? I haven’t used
LaTeX in a while...

Andrea