Builder<K, V> combine(Builder<K, V> other) {
      super.combine(other);
      return this;
    }

    @Override
    public Builder<K, V> orderEntriesByValue(Comparator<? super V> valueComparator) {
      throw new UnsupportedOperationException("Not available on ImmutableSortedMap.Builder");
    }

    @Override
    public ImmutableSortedMap<K, V> build() {
      return buildOrThrow();
    }