protected function loadCustomerRefs($dkNumber)
    {
        if (!is_null($dkNumber)) {
            $this->customerRef = new MasterPricer\CustomerRef();
            $this->customerRef->customerReferences[] = new MasterPricer\CustomerReferences(
                $dkNumber,
                MasterPricer\CustomerReferences::QUAL_AGENCY_GROUPING_ID
            );
        }
    }