private function getConceptFields(Source $source)
    {
        $fields = array();
        $fields += array(
            'send' => array(
                'type' => 'button',
                'value' => $this->t('send_again'),
                'ajax' => array(
                    'service' => 'invoice_add',
                    'parent_type' => $this->source->getType(),
                    'parent_source' => $this->source->getId(),
                    'type' => $source->getType(),
                    'source' => $source->getId(),
                    'value' => 1,
                ),
            ),
        );
        return $fields;
    }