PHP Warning: array_merge()

Hello,

I get the following error when using the plugin:

PHP message: PHP Warning: array_merge(): Expected parameter 1 to be an array, string given in /wp-content/plugins/controlled-admin-access/core/migrations/class-migration-200.php on line 57

Corresponding code:

$newUser->setCreatedBy(get_current_user_id());

$mainMenu = get_user_meta($user->ID, ‘caa_main_menu’, true);
$subMenu = get_user_meta($user->ID, ‘caa_sub_menu’, true);

$restricted_items = array_merge($mainMenu, $subMenu);

$newUser->setRestrictedMenu($restricted_items);

Please help me.
Thanks,
Milan