Broken

Warning: in_array() expects parameter 2 to be array, boolean given in /var/www/vhosts/example.com/httpdocs/wp-content/plugins/multisite-robotstxt-manager/includes/class_upgrade.php on line 508

There seems to be something wrong with this line:
if( ! in_array( "index.php?robots=1", $rules ) ) { $warning = true; }