Fixes: #50 - setWithOptions does return simple String value

[pmlopes]

Fix #50

[cescoffier]

Thinking about compatibility. I guess it's ok, as before the user would not have used the parameter:

    ...,
   ar -> { 
      // do nothing with ar.result()
   }

Now he can use it. The only weird case would be a check to null, but I guess this is more a bug in his application.

So 👍