Laravel , Voyager - Call to a member function relationLoaded() on string

I'v installed Voyager tool for Laravel , after creating a new User and try to login , I saw this

The Error

That is what I get , I've checked the role_id in the User table in the database its recorded as Null . I've to enter the role_id manually even if I changed the role from user to admin in the dashboard its not changed in the database

thats from where the error comes

So what is the problem and how can I solve it ?

via Chebli Mohamed