@Override
        protected Void doInBackground() throws Exception {
            
            // Convert known data text files to treeset dictionaries
            // (because String.hashCode() is really slow)
            dictionaries = new ArrayList<>();
            if (fields != null && !fields.isEmpty()) {
                for (int i = 0; i < fields.size(); ++i) {
                    Field f = fields.get(i);
                    TreeSet<String> dictionary = new TreeSet<>();
                    if (f.knownData() != null) {
                        if (communicationNotifier != null) {
                            String s = communicationNotifier.downloadHtml(f.knownData()).toLowerCase();
                            List<String> list = Arrays.asList(s.split(","));
                            dictionary.addAll(list);
                        }
                    }
                    dictionaries.add(dictionary);
                }
            }
            return null;
            
        }