ArrayBasedBuilder(int initialCapacity) {
      checkNonnegative(initialCapacity, "initialCapacity");
      this.contents = new @Nullable Object[initialCapacity];
      this.size = 0;
    }

    /*
     * Expand the absolute capacity of the builder so it can accept at least the specified number of
     * elements without being resized. Also, if we've already built a collection backed by the
     * current array, create a new array.