public static function get_sidebar( $post_id = null ) {

		if ( empty( $post_id ) ) {
			$post_id = get_post()->ID;
		}

		$sidebar = get_post_meta( $post_id, '_custom_sidebar_id', true );

		if ( $sidebar == false && isset( self::$default_sidebar_id ) ) {
			$sidebar = self::$default_sidebar_id;
		}

		return $sidebar;

	}