/**
  * Unfortunately, Magento does not consistently use a single path to request a customer's tax class id.
  * Therefore, we need to overwrite this function, which is called occasionally and circumvents the getTaxClassId()
  * function in Mage_Customer_Model_Customer.
  * If we are to use the Avectra Tax Exempt Status, this function never returns and we rely on the value set in
  * ICC_Customer_Model_Customer::getTaxClassId();
  *
  * @param null $groupId
  * @return mixed
  */
 public function getTaxClassId($groupId = null)
 {
     $useAvectraTaxExemptStatus = Mage::getModel('customer/customer')->useAvectraTaxExemptStatus();
     if ($useAvectraTaxExemptStatus) {
         return parent::getTaxClassId(null);
     }
     return parent::getTaxClassId($groupId);
 }