Source

File: wp-includes/widgets/class-wp-widget-links.php

public function update( $new_instance, $old_instance ) {
		$new_instance = (array) $new_instance;
		$instance     = array(
			'images'      => 0,
			'name'        => 0,
			'description' => 0,
			'rating'      => 0,
		);
		foreach ( $instance as $field => $val ) {
			if ( isset( $new_instance[ $field ] ) ) {
				$instance[ $field ] = 1;
			}
		}

		$instance['orderby'] = 'name';
		if ( in_array( $new_instance['orderby'], array( 'name', 'rating', 'id', 'rand' ), true ) ) {
			$instance['orderby'] = $new_instance['orderby'];
		}

		$instance['category'] = intval( $new_instance['category'] );
		$instance['limit']    = ! empty( $new_instance['limit'] ) ? intval( $new_instance['limit'] ) : -1;

		return $instance;
	}