protected function _serializeOptionalAmount($nodeName, $amount, $currencyCode=null)
	{
		if( $currencyCode)
		{
			return (!is_null($amount) && !is_nan($amount)) ? "<$nodeName currencyCode=\"$currencyCode\">{$this->_helper->formatAmount($amount)}</$nodeName>" : '';
		} else {
			return (!is_null($amount) && !is_nan($amount)) ? "<$nodeName>{$this->_helper->formatAmount($amount)}</$nodeName>" : '';
		}
	}