title: transformation drops documents error in R
body: <p>Whenever i run this code, tm_map line give me warning message as 
  Warning message:
  In tm_map.SimpleCorpus(docs, toSpace, "/") : transformation drops documents</p>
  
  <pre><code>texts &lt;- read.csv("./Data/fast food/Domino's/Domino's veg pizza.csv",stringsAsFactors = FALSE)
          docs &lt;- Corpus(VectorSource(texts))
          toSpace &lt;- content_transformer(function (x , pattern ) gsub(pattern, " ", x))
          docs &lt;- tm_map(docs, toSpace, "/")
          docs &lt;- tm_map(docs, toSpace, "@")
          docs &lt;- tm_map(docs, toSpace, "\\|")
          docs &lt;- tm_map(docs, content_transformer(tolower))
          docs &lt;- tm_map(docs, removeNumbers)
          docs &lt;- tm_map(docs, removeWords, stopwords("english"))
          docs &lt;- tm_map(docs, removeWords, c("blabla1", "blabla2")) 
          docs &lt;- tm_map(docs, removePunctuation)
          docs &lt;- tm_map(docs, stripWhitespace)
  </code></pre>