* use `get(key) ?: defaultValue` instead of this method, anyway.
     */
    V result = get(key);
    // TODO(b/192579700): Use a ternary once it no longer confuses our nullness checker.
    if (result != null) {
      return result;
    } else {
      return defaultValue;
    }
  }

       *
       * (And I don't believe there's any situation in which we call x.combine(y) when x is a plain
       * ImmutableSet.Builder but y is an ImmutableSortedSet.Builder (or vice versa). Certainly
       * ImmutableSortedSet.Builder.combine() is written as if its argument will never be a plain
       * ImmutableSet.Builder: It casts immediately to ImmutableSortedSet.Builder.)
       */

   * Returns 1 if {@code x < y} as unsigned longs, and 0 otherwise. Assumes that x - y fits into a
   * signed long. The implementation is branch-free, and benchmarks suggest it is measurably faster
   * than the straightforward ternary expression.
   */
  @VisibleForTesting
  static int lessThanBranchFree(long x, long y) {
    // Returns the sign bit of x - y.
    return (int) (~~(x - y) >>> (Long.SIZE - 1));
  }

  /**