Exclude categories from wp query not working

Found the answer so it can benefit someone else

$posts = get_posts(array(
    'post_type' => 'exhibition',
    'tax_query' => array(
            array(
                'taxonomy' => 'categories_for_exhibitions',
                'field'    => 'slug',
                'terms'    => 'current',
                operator => 'NOT IN',
            ),
        )

));