Having problem with twitterR, language cannot be defined

Question

I have been reviewing an online R class. The data Science and machine learning with R, I am doing the natural language processing part.

I was following the code as follows:

library(twitteR) 
library(tm) 
library(wordcloud) 
library(RColorBrewer)

setup_twitter_oauth(consumerKey, consumerSecret, accessToken, accessTokenSecret) 
[1] "Using direct authentication"

searchTwitteR("soccer", n=1000, lang = "en")

However, the language can not be defined. I got an error as : Error: invalid assignment for reference class field ‘language’, should be from class “character” or a subclass (was class “NULL”)

Anyone can help? Thank you very much.