public function getCustomerReference()
    {
        if (isset($this->data['object']) && 'customer' === $this->data['object']) {
            return $this->data['id'];
        }
        if (isset($this->data['object']) && 'transaction' === $this->data['object']) {
            if (! empty($this->data['customer'])) {
                return $this->data['customer']['id'];
            }
        }
        if (isset($this->data['object']) && 'card' === $this->data['object']) {
            if (! empty($this->data['customer'])) {
                return $this->data['customer']['id'];
            }
        }

        return null;
    }