Error in check_input(x):

[codersv69]

I encounter the following error when I run this code:
Error in check_input(x) :
Input must be a character vector of any length or a list of character
vectors, each of which has a length of 1.

stock_tokens
Error: object 'stock_tokens' not found

The line of code with the unnest_tokens() function seems to be where the error is generated. What might be causing this error?

library(tidyr)
library(dplyr)
#>
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#>
#> filter, lag
#> The following objects are masked from 'package:base':
#>
#> intersect, setdiff, setequal, union
library(tidytext)
library(tidyverse)
#> -- Attaching packages -------------------------------- tidyverse 1.2.1 --
#> v ggplot2 2.2.1 v purrr 0.2.5
#> v tibble 1.4.2 v stringr 1.3.1
#> v readr 1.1.1 v forcats 0.3.0
#> -- Conflicts ----------------------------------- tidyverse_conflicts() --
#> x dplyr::filter() masks stats::filter()
#> x dplyr::lag() masks stats::lag()
library(tm.plugin.webmining)
#>
#> Attaching package: 'tm.plugin.webmining'
#> The following object is masked from 'package:tidyr':
#>
#> extract
#> The following object is masked from 'package:base':
#>
#> parse
library(purrr)

company <- c("Microsoft", "Apple", "Google", "Amazon", "Facebook")
symbol <- c("MSFT", "AAPL", "GOOG", "AMZN", "FB")

download_articles <- function(symbol) {
WebCorpus(YahooFinanceSource(paste0("NASDAQ:", symbol)))

}

stock_articles <- data_frame(company = company,
symbol = symbol) %>%
mutate(corpus = map(symbol, download_articles))

stock_articles
#> # A tibble: 5 x 3
#> company symbol corpus
#>
#> 1 Microsoft MSFT <S3: WebCorpus>
#> 2 Apple AAPL <S3: WebCorpus>
#> 3 Google GOOG <S3: WebCorpus>
#> 4 Amazon AMZN <S3: WebCorpus>
#> 5 Facebook FB <S3: WebCorpus>

stock_tokens <- stock_articles %>%
unnest(map(corpus, tidy)) %>%
unnest_tokens(word, text) %>%#encounter input error on this line of code
select(company, datetimestamp, word, id, heading)
#> Error in check_input(x): Input must be a character vector of any length or a list of character
#> vectors, each of which has a length of 1.

stock_tokens
#> Error in eval(expr, envir, enclos): object 'stock_tokens' not found