> According to the definition of comment-line-break-function:
> The function should take a single optional argument, which is a flag
> indicating whether it should use soft newlines.
> But in nxml-mode:
> (setq-local comment-line-break-function #'nxml-newline-and-indent)
> (defun nxml-newline-and-indent (soft) ...)
> Could you please make an argument optional?
I've made this change on master; the fix will be in Emacs 28.1.