Save checkboxes

<?php
add_action('save_post', 'save_couponbooks');

function save_couponbooks($post_id) {
	global $post;
	if ($post->post_type != "coupon" || ( defined('DOING_AUTOSAVE') && DOING_AUTOSAVE ) || !current_user_can( 'edit_coupon', $post->ID )) {
			return $post->ID;
	}
	$couponbooks = array();
	foreach($_POST['tax_input']['couponbook'] as $couponbook) {
		if (is_numeric($couponbook)) {
			$couponbook = get_term($couponbook, 'couponbook');
			if (!is_wp_error($couponbook)) {
				$couponbooks[] = $couponbook->slug;
			}
		}
	}
	wp_set_object_terms($post->ID, $couponbooks, 'couponbook', false);
}
?>