code: @Override
    public Selection<E> value() {
      return value == null ? null : new Selection<E>() {
        @Override
        public E result() {
          return value;
        }
  
        @Override
        public Object target() {
          return target;
        }
      };
    }
docs: Returns the selection object only if the result is a non-null value. A {@code null}
  value will be returned if this selection's result is {@code null}.
  
  @return the selection object.