• Map.getOrDefault method could be used to replace the code like this:

        aValue = map.get(aKey);
        if (aValue == null) {
          aValue = "none";
        }
      

• Map.computeIfAbsent method could be used to replace the code like this:

        List<String> list = map.get(key);
        if (list == null) {
          list = new ArrayList<>();
          map.put(key, list);
        }
      

This conversion is available since Java 8 only.