code: public function updateCustomerGroupAndCurrency()
      {
          if (!$this->hasCart() || $this->cart->isLocked()) {
              return $this;
          }
  
          // Customer group
          if (null !== $customer = $this->cart->getCustomer()) {
              if ($this->cart->getCustomerGroup() !== $customer->getCustomerGroup()) {
                  $this->cart->setCustomerGroup($customer->getCustomerGroup());
              }
          }
  
          // Sets the default customer group
          if (null === $this->cart->getCustomerGroup()) {
              $this->cart->setCustomerGroup($this->customerProvider->getCustomerGroup());
          }
  
          // Sets the currency
          if (null === $this->cart->getCurrency()) {
              $this->cart->setCurrency($this->currencyProvider->getCurrency());
          }
  
          return $this;
      }
docs: Updates the cart customer group and currency.
  
  @return $this