code: private function isIdentityValid(SaleInterface $cart)
      {
          return 0 < strlen($cart->getEmail())
              && 0 < strlen($cart->getGender())
              && 0 < strlen($cart->getFirstName())
              && 0 < strlen($cart->getLastName());
      }
docs: Returns whether the sale identity fields are valid.
  
  @param SaleInterface $cart
  
  @return bool