Oracle treats the empty string as a NULL and so fails the NOT NULL requirement.

$url defaults to the empty string and so hits this problem.
$info also had this problem but was fixed in
revision 1.348

add_to_log just needs a similar fix for $url, i.e.

 if ($CFG->type = 'oci8po') { 

 	  	         if (empty($info)) {

 	  	             $info = ' ';

 	  	         }

+	  	         if (empty($url)) {

+	  	             $url = ' '; 

+	  	         }

 }