code: public void writeLines(Iterable<? extends CharSequence> lines, String lineSeparator)
        throws IOException {
      checkNotNull(lines);
      checkNotNull(lineSeparator);
  
      Closer closer = Closer.create();
      try {
        Writer out = closer.register(openBufferedStream());
        for (CharSequence line : lines) {
          out.append(line).append(lineSeparator);
        }
        out.flush(); // https://code.google.com/p/guava-libraries/issues/detail?id=1330
      } catch (Throwable e) {
        throw closer.rethrow(e);
      } finally {
        closer.close();
      }
    }
docs: Writes the given lines of text to this sink with each line (including the last) terminated with
  the given line separator.
  
  @throws IOException if an I/O error occurs while writing to this sink