Solution # 1 - Enum function

[gianlucatomasino]

No description provided.

[arialdomartini]

Smart solution!
I didn't know that enum had that capability! It is really impressive!

It's apparent that the hardest part is the default execution path of the switch statement. @gianlucatomasino used a try/catch (which is somehow a hidden if)
I used a DefaultedMap and, guess what? Yes! It contains an if

  public Object More ...get(Object key) {
        // create value for key if key is not currently in the map
        if (map.containsKey(key) == false) {
            if (value instanceof Transformer) {
                return ((Transformer) value).transform(key);
            }
            return value;
        }
        return map.get(key);
    }