Error during unserialization in Order/Payment.php: Mage_Core_Helper_UnserializeArray->unserialize('NULL\n')

Question

Getting error on exception log,How to fix this?

Using: Magento ver. 1.9.3.1

exception 'Exception' with message 'Error during unserialization' in /home/testing/public_html/lib/Unserialize/Parser.php:60
Stack trace:
#0 /home/testing/public_html/app/code/core/Mage/Core/Helper/UnserializeArray.php(44): Unserialize_Parser->unserialize('NULL\n')
#1 /home/testing/public_html/app/code/core/Mage/Sales/Model/Resource/Order/Payment.php(78): Mage_Core_Helper_UnserializeArray->unserialize('NULL\n')
#2 /home/testing/public_html/app/code/core/Mage/Core/Model/Resource/Db/Abstract.php(550): Mage_Sales_Model_Resource_Order_Payment->_unserializeField(Object(Mage_Sales_Model_Order_Payment), 'additional_info...', Array)
#3 /home/testing/public_html/app/code/core/Mage/Sales/Model/Resource/Order/Payment/Collection.php(68): Mage_Core_Model_Resource_Db_Abstract->unserializeFields(Object(Mage_Sales_Model_Order_Payment))
#4 /home/testing/public_html/app/code/local/Varien/Data/Collection/Db.php(612): Mage_Sales_Model_Resource_Order_Payment_Collection->_afterLoad()
#5 /home/testing/public_html/lib/Varien/Data/Collection.php(741): Varien_Data_Collection_Db->load()
#6 /home/testing/public_html/app/code/local/Mage/Sales/Model/Order.php(1673): Varien_Data_Collection->getIterator()
#7 /home/testing/public_html/app/code/local/Mage/Sales/Model/Order.php(907): Mage_Sales_Model_Order->getPaymentsCollection()
#8 /home/testing/public_html/app/code/community/Ds/Imports/Model/Functional/Export.php(7): Mage_Sales_Model_Order->getPayment()
#9 /home/testing/public_html/app/code/community/Ds/Imports/Model/Table/Csvcontent.php(104): Ds_Imports_Model_Functional_Export->getPaymentMethod(Object(Mage_Sales_Model_Order))
#10 /home/testing/public_html/app/code/community/Ds/Imports/Model/Selectorder.php(95): Ds_Imports_Model_Table_Csvcontent->getCSVvalue(Object(Mage_Sales_Model_Order))
#11 /home/testing/public_html/app/code/community/Ds/Imports/Model/Selectorder.php(77): Ds_Imports_Model_Selectorder->writeOrder(Object(Mage_Sales_Model_Order), Resource id #260)
#12 /home/testing/public_html/app/code/community/Ds/Imports/controllers/Adminhtml/ExportsController.php(35): Ds_Imports_Model_Selectorder->selectOrdersdownload(Array)
#13 /home/testing/public_html/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Ds_Imports_Adminhtml_ExportsController->selectorderAction()
#14 /home/testing/public_html/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action->dispatch('selectorder')
#15 /home/testing/public_html/app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#16 /home/testing/public_html/app/code/core/Mage/Core/Model/App.php(365): Mage_Core_Controller_Varien_Front->dispatch()
#17 /home/testing/public_html/app/Mage.php(684): Mage_Core_Model_App->run(Array)
#18 /home/testing/public_html/index.php(113): Mage::run('', 'store')
#19 {main}

Thanks