Undefined index: carriers in /var/www/solar/include/classes/system.php:151

Error line in /var/www/solar/include/classes/system.php:
000147 	                
000148 	                $source_empire = new Empire($this->DB,$GAME["template"],$GAME["gameplay_costs"]);
000149 	                $source_empire->load($rs->fields["empire_from"]);
000150 	                $source_empire->army->data["carriers"] += $rs->fields["carriers"];
000151 	                $source_empire->save();
000152 	                
000153 	                // send notifications

Execution backtrace:
/var/www/solar/include/classes/system.php:151 	handletradeconvoys()
/var/www/solar/include/classes/system.php:78 	handletradeconvoys(447)
/var/www/solar/include/init.php:118 	init()
/var/www/solar/login.php:40 	require_once(/var/www/solar/include/init.php)