Unquoted Unicode strings seems to not parse as “bad argument”

[toastal]

See: processone/ejabberd#4559

I was trying to use this in an Ejabberd config

modules:
   mod_invites:
      # Using typographically-correct apostrophe;
      # `'` is incorrect.
      site_name: toastal’s XMPP Server

failing with

2026-04-03 19:55:31.393837+07:00 [critical] <0.119.0>@ejabberd_app:start/2:79 Failed to start ejabberd application: Exception occurred during configuration processing. This is most likely due to faulty/incompatible validator in third-party code. If you are not running any third-party code, please report the bug with ejabberd configuration file attached and the following stacktrace included:
** exception error: bad argument
   in function  iolist_to_binary/1
      called as iolist_to_binary([116,111,97,115,116,97,108,8217,115,32,88,77,
                                  80,80,32,83,101,114,118,101,114,32,105,110,
                                  32,84,104,97,105,108,97,110,100])
      *** argument 1: not an iodata term
   in call from ejabberd_config:replace_keywords/3 (/build/source/src/ejabberd_config.erl:440)
   in call from yconf:'-and_then/2-fun-0-'/3 (yconf.erl:620)
   in call from yconf:validate_option/3 (yconf.erl:1281)
   in call from yconf:validate_options/8 (yconf.erl:1258)
   in call from yconf:'-and_then/2-fun-0-'/3 (yconf.erl:620)
   in call from yconf:validate_option/3 (yconf.erl:1281)
   in call from yconf:validate_options/8 (yconf.erl:1258)

Trying to use Ejabberd config macros, including EJABBERD_MACRO_INVITES_SITE_NAME="toastal’s XMPP Server", also did not work failing on the typographically-correct apostrophe here (the one called 8217). Similar had happened when I tried characters outside the Latin set (such as CJK), but as far as I can tell, these should not require string quoting in YAML like key: "ผิดพลาด" instead of key: ผิดพลาด (this string also fails in the site_name).