public function addCategory(\Magento\Framework\DataObject $customer)
    {
        $email = strtolower(trim($customer->getEmail()));
        if (!isset($this->_customerIds[$email])) {
            $this->_customerIds[$email] = [];
        }
        $this->_customerIds[$email][$customer->getWebsiteId()] = $customer->getId();

        return $this;
    }