Accept null as a parameter for Sanctum@getAccessTokenFromRequestUsing()

[cosmastech]

Have a kind of an odd case where we're communicating between two applications and want to only allow for authorizing via Sanctum (on one endpoint) with a custom method of getting the access token. (The original app uses Passport, the new app uses Sanctum, so the HasApiTokens traits conflict on the User model).

use App\Http\Controllers\Controller;
use Illuminate\Http\Request;
use Laravel\Sanctum\Sanctum;

class SwapTokenController extends Controller
{
    public function __invoke(SwapTokenRequest $request)
    {
        $originalCallback = Sanctum::$accessTokenRetrievalCallback ?? null;

        try {
            Sanctum::getAccessTokenFromRequestUsing(function (Request $request) {
                if (! $sanctumTokenString = $request->get('sanctum_token')) {
                    return null;
                }

                return $sanctumTokenString;
            });

            /** @var User|null $user */
            $sanctumGuard = app('auth')->guard('sanctum');
            $user = $sanctumGuard->user();

            // some other fun stuff here
        } finally {
            Sanctum::$accessTokenRetrievalCallback = $originalCallback;
        }
    }
}

$originalCallback is currently null for our app. It seems kind of weird that we can't just call Sanctum::getAccessTokenFromRequestUsing($originalCallback) instead of having to set the static property on the Sanctum object.