R function not returning corpus

I have created a function to clean the corpus

#function to clean corpus
clean_corpus <- function(df, dfcol) {
  wordCorpus <- VCorpus(VectorSource(data.table(df$dfcol)))                                                      #create corpus
  wordCorpus <- tm_map(wordCorpus, content_transformer(stripWhitespace))                                       #remove whitespace
  wordCorpus <- tm_map(wordCorpus, content_transformer(tolower))                                               #convert to lowercase
  wordCorpus <- tm_map(wordCorpus, content_transformer(removeWords), c(stopwords('english'), 'john', 'james')) #remove stopwords 

  #replace foreign characters like "âë" to "'" to be removed in remove punctuation step
  removeForeignChar <- function(x) gsub("[^0-9A-Za-z///' ]","'" , x ,ignore.case = TRUE)
  wordCorpus <- tm_map(wordCorpus, content_transformer(removeForeignChar))

  wordCorpus <- tm_map(wordCorpus, content_transformer(removePunctuation))    #remove punctuations
  wordCorpus <- tm_map(wordCorpus, content_transformer(removeNumbers))        #remove numbers
  removeURL <- function(x) gsub("http[[:alnum:]]*",'',x)                      #function to remove URLs
  wordCorpus <- tm_map(wordCorpus, content_transformer(removeURL))            #remove URLs

  return(wordCorpus)
}

Then I apply it to a dataframe called 'usvideos' and column 'title'

titleCorpus <- clean_corpus(usvideos, title)

However, when I check titleCorpus, I find that it is empty. How do I solve this problem?