* more convenient.
   *
   * <p>Builder instances can be reused - it is safe to call {@link #buildOrThrow} multiple times to
   * build multiple maps in series. Each map is a superset of the maps created before it.
   *
   * @since 2.0
   */
  public static class Builder<K, V> extends ImmutableMap.Builder<K, V> {
    private transient @Nullable Object[] keys;

   * more convenient.
   *
   * <p>Builder instances can be reused - it is safe to call {@link #buildOrThrow} multiple times to
   * build multiple maps in series. Each map is a superset of the maps created before it.
   *
   * @since 2.0
   */
  public static class Builder<K, V> extends ImmutableMap.Builder<K, V> {
    private final Comparator<? super K> comparator;

    return new ImmutableSortedMap<K, V>(delegate, comparator);
  }

  /*
   * We don't permit nulls, but we wrap every comparator with nullsFirst().
   * Why? We want for queries like containsKey(null) to return false, but the
   * GWT SortedMap implementation that we delegate to throws
   * NullPointerException if the comparator does. Since our construction