Fixing session manager method name, node and role ID handling

Not sure how the nid->value() code was tested, but that has to be a fatal error as value is a property, not a method. And assigning to ->nid doesn't change anything, it is still a FieldItemList object.

So, instead of that, using a similar pattern as we do for $user, keep $node as a stdClass object and just assign the nid.