code: static <E> ImmutableList<E> unsafeDelegateList(List<? extends E> list) {
      switch (list.size()) {
        case 0:
          return of();
        case 1:
          return of(list.get(0));
        default:
          @SuppressWarnings("unchecked")
          List<E> castedList = (List<E>) list;
          return new RegularImmutableList<E>(castedList);
      }
    }
docs: are guaranteed to be non-null.