* ImmutableSortedMap#orderedBy}.
     */
    public Builder(Comparator<? super K> comparator) {
      this(comparator, ImmutableCollection.Builder.DEFAULT_INITIAL_CAPACITY);
    }

    private Builder(Comparator<? super K> comparator, int initialCapacity) {
      this.comparator = checkNotNull(comparator);
      this.keys = new @Nullable Object[initialCapacity];