code: public static void writeStringSet(DataOutputStream os, Collection<String> set) throws IOException {
  		if(set==null) {
  			os.writeInt(-1);
  		} else {
  			os.writeInt(set.size());
  			for(String s : set) {
  				writeString(os, s);
  			}
  		}
  
  	}
docs: Write a set with proper sizing
  
  Note: at the moment, this is just String.  Probably can develop system where types
  are supported too... but not now.
  
  @param os
  @param set
  @throws IOException