I am getting the following error - can anyone advice on the solutions please?

PHP Warning: Creating default object from empty value in /home/XXXX/public_html/includes/modules/payment/sagepay_form.php on line 734
[13-Aug-2014 03:05:54 America/Phoenix] PHP Warning: Creating default object from empty value in /home/XXXX/public_html/includes/modules/payment/sagepay_form.php on line 734

This is the code in line 734

if ($start !== false){
$tokens_found[$i]->start = $start;
$tokens_found[$i]->token = $tokens[$i];
}