Problem/Motivation I am using Flag 8.x-4.0-beta3 in Drupal 9.46 with PHP 7.416

I am looking to upgrade my hosting ASAP to PHP 8.x but as a test on my local development site I've updated (highest I can go locally) to PHP 8.1.0.

When I do so I see the following errors from the Flag module...

Deprecated function: str_replace(): Passing null to parameter #2 ($replace) of type array|string is deprecated in Drupal\Core\Access\RouteProcessorCsrf->processOutbound() (line 41 of core\lib\Drupal\Core\Access\RouteProcessorCsrf.php). Drupal\Core\Access\RouteProcessorCsrf->processOutbound('flag.action_link_flag', Object, Array, Object) (Line: 52) Drupal\Core\RouteProcessor\RouteProcessorManager->processOutbound('flag.action_link_flag', Object, Array, Object) (Line: 404) Drupal\Core\Routing\UrlGenerator->processRoute('flag.action_link_flag', Object, Array, Object) (Line: 291) Drupal\Core\Routing\UrlGenerator->generateFromRoute('flag.action_link_flag', Array, Array, 1) (Line: 105) Drupal\Core\Render\MetadataBubblingUrlGenerator->generateFromRoute('flag.action_link_flag', Array, Array, 1) (Line: 765) I cannot see any obvious discussions RE Flag and PHP 8.x and of course I do realise that the module is only in Beta and therefore not strictly to be used but it is a key player on ours (and I'm sure many other sites) so I wanted to ask about this here in the forum.

Thankyou