docs: public static <S> List<S> of(S left, List<? extends S> right) {
          if (right.isEmpty()) {
              return Collections.singletonList(left);
          } else {
              List<S> list = new ArrayList<S>(1 + right.size());
              list.add(left);
              list.addAll(right);
              return list;
          }
      }