Access session from global scope within service class

Hi! so within my application users may belong to a company (yet only one; in future during the login the user might choose the company to work on). Sure thing, all related objects/models relate to the company as well, so other users may access those as well (Assume, documents/appointments/... that belong to that company).

So to keep code clean I introduced global scopes on those company related models:

protected static function booted() {
    static::addGlobalScope(new CompanyScope);
}

class CompanyScope implements Scope {
    public function apply(Builder $builder, Model $model) {
        $builder->where('company_id', session(SessionKey::SESSION_KEY_COMPANY_ID));
    }
}

while the session key is set during login. Great thing and working perfectly.

I stumpled accross this neat repo: https://github.com/alexeymezenin/laravel-best-practices/, and started to migrate some logic into services.

class DocumentService
{
    private $docInstance;

    public function __construct(DocumentType $type)
    {
        $this->docInstance = Document::where('type', $type->value)->first();
    }

    public function nextNumber()
    {
        return $this->docInstance->getNextNumber();
    }
}

Documents are "numbered", but once my Controller tries to obtain the nextNumber(), the call fails, since $docInstance is null. The exception page tells me, that the query on Document is searching for company_id is null; so likely the service doesn't have access to the session scope. I guess "works as designed" but I am not able to cope with a new solution.

Does one of you has some hint how to approach/solve this issue?

Thanks!