code: public <T> boolean isNone
              (final Optional<T> optional)
          {
          final OptionalVisitor<Boolean,T> visitor =
                  new OptionalVisitor<Boolean,T> ()
              {
              public Boolean visitNone
                      (final None<T> none)
                  {
                  return true;
                  }
  
              public Boolean visitSome
                      (final Some<T> some)
                  {
                  return false;
                  }
              };
  
          return optional.accept(visitor);
          }
docs: {@inheritDoc}