*     might be the keys' natural order)
     * @since 31.0
     */
    @Override
    @SuppressWarnings("unchecked") // see inline comments
    public ImmutableSortedMap<K, V> buildOrThrow() {
      switch (size) {
        case 0:
          return emptyMap(comparator);
        case 1:
          // We're careful to put only K and V instances in.

      // threshold is equal to ceilingPowerOfTwo(expectedSize). There is a separate code
      // path when the first operation on the new map is putAll(otherMap). There, prior to
      // https://github.com/openjdk/jdk/commit/3e393047e12147a81e2899784b943923fc34da8e, a bug
      // meant that sometimes a too-large threshold is calculated. However, this new threshold is