Invalid argument??

Hi, when I start the advanced kits plugin, modified by me, I receive this error in console:

[Server] Server thread/INFO Enabling AdvancedKits v5.1.1
[Server] Server thread/CRITICAL ErrorException: "Invalid argument supplied for foreach()" (EXCEPTION) in "AdvancedKits_dev-23.phar/src/AdvancedKits/Main" at line 96
[Server] Server thread/DEBUG #0 AdvancedKits_dev-23.phar/src/AdvancedKits/Main(96): pocketmine\error_handler(integer 2, string Invalid argument supplied for foreach(), string phar:///plugins/AdvancedKits_dev-23.phar/src/AdvancedKits/Main.php, integer 96, array Array())


The code for the line which is probably causing the issue is this:
private function fixConfig(&$config){
foreach($config as $name => $kit){
if(isset($kit["users"])){
$users = array_map("strtolower", $kit["users"]);
$config[$name]["users"] = $users;


Could someone please say what is going wrong here

 

$config is an array?