Produces error in nextcloud logs reduce_string_array(): Implicitly marking parameter $remove_short_values as nullable is deprecated

[mdlaat]

Thank you for vdirsyncer

Syncing from google to nextcloud
The starts and seems to work but eventually creates an error:
Unknown error occurred for {redacted}: Cannot connect to host {redacted}:443 ssl:default [Connect call failed ({redacted}, 443)]

In nextcloud logs, a more descriptive error is displayed:
voku\helper\UTF8::reduce_string_array(): Implicitly marking parameter $remove_short_values as nullable is deprecated, the explicit nullable type must be used instead at /config/www/nextcloud/apps/mail/vendor/voku/portable-utf8/src/voku/helper/UTF8.php#13827

Any workaround?
Thank you

[WhyNotHugo]

I've no idea what the error means. I'm not sure that the log which you're seeing is related to the connection failure.

Can you reach the nextcloud instance over https from the same host running vdirsyncer?

[mdlaat]

Yes, I can reach nextcloud. Discovery is fine.
I get only that error in the log at the same moment as vdirsyncer tries to write to the calendar. It must be related.