Ok, I succeeded at removing all the conditional paths, but the resulting code is both much longer and (maybe) awful.

The idea is: the 3 paths are encapsulated into 3 separate classes, all sharing the same interface Strategy: we have

• the NullStrategy returning null
• the DoubleStrategy returning the string repeated twice
• the ErrorStrategy returning the string error.

The class Formatter asks for permission, as usual, then asks for the the right strategy (based on the received permission) from the lookup dictionary

String response = service.askForPermission();
Strategy strategy = strategies.get(response);

and then it delegates the execution of the job to the selected strategy

return strategy.workOn(theInput);

As you see, no ifs at all.

Two notes:

1. The Formatter is completely unaware of which strategy is used, since it's completely decoupled from it (it knows the strategy only in terms of interface)
2. As @peachofpersia noted, there's a hidden if in the use of DefaultedMap.

Is it a better design than the orginal one? I wonder. I'm looking forward to hearing from you.