code: public static <T> Function<Optional<T>, T> getFunction() {
      return new Function<Optional<T>, T>() {
        @Override
        public T apply(final Optional<T> input) {
          return input.get();
        }
      };
    }
docs: Guava {@link Function} to call {@link Optional#get()}; this will throw an {@link
  IllegalStateException} if the input is {@link Optional#absent()}.