code: @Override
    @SuppressWarnings("unchecked")
    public Class<W> getWritableClass() throws IOException {
      if (writable == null) {
        return null;
      }
      return (Class<W>) writable.getClass();
    }
docs: Default implementation returns value of {@link #writableClass}.
  
  @see com.twitter.elephantbird.pig.util.WritableConverter#getWritableClass()