R Error in tolower() invalid multibyte string using DocumentTermMatrix

https://stackoverflow.com/questions/13187605/error-in-tolower-invalid-multibyte-string

# to avoid datatables warning: error in tolower(x) invalid multibyte string
# assuming all columns are char
new_data <- as.data.frame(
  lapply(old_data, enc2utf8),
  stringsAsFactors = FALSE
)