I'm doing network meta analysis. The code:

library(lattice)
library(coda)
library(codetools)
library(gemtc)
library(R2OpenBUGS)
library(igraph)
library(meta)
fileName <- system.file('extdata/luades-smoking.gemtc',package='gemtc')
network <- read.mtc.network(fileName)
model <- mtc.model(network)
result <- mtc.run(model)
forest(result)
Error in UseMethod("forest") : 
  no applicable method for 'forest' applied to an object of class "mtc.result"

How to solve：no applicable method for 'forest' applied to an object of class "mtc.result" ?