PHP 8.1 compatibility

Problem/Motivation

Deprecated function: preg_match(): Passing null to parameter #2 ($subject) of type string is deprecated in Drupal\oauth\Authentication\Provider\OAuthDrupalProvider->applies() (line 63 of modules/contrib/oauth/src/Authentication/Provider/OAuthDrupalProvider.php).
Drupal\oauth\Authentication\Provider\OAuthDrupalProvider->applies(Object) (Line: 103)
Drupal\Core\Authentication\AuthenticationManager->getProvider(Object) (Line: 41)
Drupal\Core\Authentication\AuthenticationManager->applies(Object) (Line: 76)
Drupal\Core\EventSubscriber\AuthenticationSubscriber->onKernelRequestAuthenticate(Object, 'kernel.request', Object)
call_user_func(Array, Object, 'kernel.request', Object) (Line: 142)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch(Object, 'kernel.request') (Line: 134)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 80)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 58)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 106)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 85)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 44)
Drupal\services\StackMiddleware\FormatSetter->handle(Object, 1, 1) (Line: 50)
Drupal\ban\BanMiddleware->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 709)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)