Collector<T, ?, ImmutableMap<K, V>> toImmutableMap(
          Function<? super T, ? extends K> keyFunction,
          Function<? super T, ? extends V> valueFunction) {
    throw new UnsupportedOperationException();
  }

  /**
   * Not supported. This method does not make sense for {@code BiMap}. This method exists only to
   * hide {@link ImmutableMap#toImmutableMap(Function, Function, BinaryOperator)} from consumers of

  /**
   * Not supported. Use {@link #toImmutableSortedMap}, which offers better type-safety, instead.
   * This method exists only to hide {@link ImmutableMap#toImmutableMap} from consumers of {@code
   * ImmutableSortedMap}.
   *
   * @throws UnsupportedOperationException always
   * @deprecated Use {@link ImmutableSortedMap#toImmutableSortedMap}.