while (elements.hasNext()) {
        add(elements.next());
      }
      return this;
    }

    @CanIgnoreReturnValue
    @SuppressWarnings("unchecked") // ArrayBasedBuilder stores its elements as Object.
    Builder<E> combine(Builder<E> other) {
      if (hashTable != null) {
        for (int i = 0; i < other.size; ++i) {