Lens for Optional<T> types

Please describe a summary of the new feature (in a paragraph):

Binding to Optional<T> type allows detecting whether this option is defined or 
undefined.  

class A {
  @Option(symbol="p", description="port number")
  Optional<Integer> port; 
}

if(port.isUndefined()) 
  port.set(8989); // default value

Please provide any additional information below:

Original issue reported on code.google.com by taroleo on 27 Feb 2011 at 1:43

RawrUniversal / xerial

Lens for Optional<T> types #92