Note.php

<?php

class Ebizmarts_SageOne_Block_Adminhtml_Sales_Order_Creditnote_Note extends Mage_Core_Block_Template {


    public function getCreditMemo() {
        return Mage::registry('current_creditmemo');
    }

    /**
     * Render block HTML
     *
     * @return string
     */
    protected function _toHtml() {

        //Return empty if invoiceId is not present
        if(!is_null($this->getCreditMemo()) && !is_null($this->getCreditMemo()->getInvoice()) && !$this->getCreditMemo()->getInvoice()->getSageoneInvoiceId()) {
            return '';
        }

        return parent::_toHtml();
    }

}