bp_get_notifications_unread_permalink( int $user_id )

	function bp_get_notifications_unread_permalink( $user_id = 0 ) {
		if ( 0 === $user_id ) {
			$user_id = bp_loggedin_user_id();
			$domain  = bp_loggedin_user_domain();
		} else {
			$domain = bp_core_get_user_domain( (int) $user_id );
		}

		$retval = trailingslashit( $domain . bp_get_notifications_slug() . '/unread' );

		/**
		 * Filters the unread notifications permalink.
		 *
		 * @since BuddyPress 1.9.0
		 * @since BuddyPress 2.6.0 Added $user_id as a parameter.
		 *
		 * @param string $retval  Permalink for the unread notifications.
		 * @param int    $user_id The user ID.
		 */
		return apply_filters( 'bp_get_notifications_unread_permalink', $retval, $user_id );
	}