code: public function normalize($customer, $format = null, array $context = [])
      {
          if ($format === 'csv' && $this->contextHasGroup('TableExport', $context)) {
              return (string)$customer;
          }
  
          $data = parent::normalize($customer, $format, $context);
  
          $parent = $customer->getParent();
  
          if ($this->contextHasGroup(['Default', 'Customer', 'Search', 'Summary'], $context)) {
              $data = array_replace($data, [
                  'number'     => $customer->getNumber(),
                  'company'    => $customer->getCompany(),
                  'email'      => $customer->getEmail(),
                  'first_name' => $customer->getFirstName(),
                  'last_name'  => $customer->getLastName(),
                  'phone'      => $this->normalizeObject($customer->getPhone(), $format, $context),
                  'mobile'     => $this->normalizeObject($customer->getMobile(), $format, $context),
                  'parent'     => $parent ? $parent->getId() : null,
                  'currency'   => $customer->getCurrency()->getCode(),
                  'locale'     => $customer->getLocale(),
              ]);
          }
  
          if ($this->contextHasGroup('Summary', $context)) {
              $payment = $parent ? $parent : $customer;
  
              $data = array_replace($data, [
                  'group'               => (string)$customer->getCustomerGroup(),
                  'parent'              => (string)$parent,
                  'vat_number'          => $payment->getVatNumber(),
                  'vat_valid'           => $payment->isVatValid(),
                  'payment_term'        => (string)$payment->getPaymentTerm(),
                  'outstanding_limit'   => $payment->getOutstandingLimit(),
                  'outstanding_balance' => $payment->getOutstandingBalance(),
                  'credit_balance'      => $payment->getCreditBalance(),
                  'description'         => $payment->getDescription(),
              ]);
          }
  
          return $data;
      }
docs: @inheritdoc
  
  @param CustomerInterface $customer