Argument error

[johnywind]

in a Symfony project, after upgrading to v4.0 I get this error:

Argument 6 passed to Auth0\JWTAuthBundle\Security\Auth0Service::__construct() must be of the type string or null, array given,
called in /srv/cache/bdd/ContainerWPjxspi/getJwtAuth_Auth0ServiceService.php on line 9
at vendor/auth0/jwt-auth-bundle/src/Security/Auth0Service.php:112)"} []

As far as I can tell, Argument 6 is the algoritm, which falls back to RS256 anyway.
Any ideea why this error occurs?