code: public FilterStreamParameters follow(long follow) {
  		if (this.follow.length() > 0) {
  			this.follow.append(',');
  		}
  		this.follow.append(follow);
  		return this;
  	}
docs: Add a user to follow in the stream.
  Does not replace any existing follows in the filter.
  @param follow the Twitter user ID of a user to follow in the stream.
  @return this FilterStreamParameters for building up filter parameters.