docs: public void put(String key, ArrayList<String> value) {
      Iterator<Pair<String, ArrayList<String>>> it = store.iterator();
      while (it.hasNext()) {
        Pair<String, ArrayList<String>> pair = it.next();
        if (key.equals(pair.first)) {
          pair.second = value;
          return;
        }
      }
      store.add(new Pair<>(key, value));
    }