public function countCustomers($criteria = null, $distinct = false, ConnectionInterface $con = null)
    {
        if (null === $this->collCustomers || null !== $criteria) {
            if ($this->isNew() && null === $this->collCustomers) {
                return 0;
            } else {
                $query = CustomerQuery::create(null, $criteria);
                if ($distinct) {
                    $query->distinct();
                }

                return $query
                    ->filterByCustomerGroup($this)
                    ->count($con);
            }
        } else {
            return count($this->collCustomers);
        }
    }