* Anyway, the purpose of this method is to implement a BinaryOperator combiner for a Collector,
     * so its return value will get used naturally.
     */
    @SuppressWarnings("CanIgnoreReturnValueSuggester")
    Builder<K, V> combine(ImmutableSortedMap.Builder<K, V> other) {
      ensureCapacity(size + other.size);
      System.arraycopy(other.keys, 0, this.keys, this.size, other.size);