public function getProject(CNabuCustomer $nb_customer = null, $force = false)
    {
        if ($nb_customer !== null && ($this->nb_project === null || $force)) {
            $this->nb_project = null;
            if ($this instanceof CNabuDataObject && $this->contains(NABU_PROJECT_FIELD_ID)) {
                $this->nb_project = $nb_customer->getProject($this);
            }
        }

        return $this->nb_project;
    }