code: @Override
  	public String isValidID(String id) {
  		Data data;
  		try {
  			data = identities.find(id, identities.reuse());
  		} catch (IOException e) {
  			return getName() + " could not lookup " + id + ": " + e.getLocalizedMessage();
  		}
  		return data==null?id + "is not an Identity in " + getName():null;
  	}
docs: Note: Return a null if found; return a String Message explaining why not found.