code: @Deprecated
    public static <T, K, V> Collector<T, ?, ImmutableMap<K, V>> toImmutableMap(
        Function<? super T, ? extends K> keyFunction,
        Function<? super T, ? extends V> valueFunction) {
      throw new UnsupportedOperationException();
    }
docs: Not supported. Use {@link ImmutableBiMap#toImmutableBiMap} instead. This method exists only to
  hide {@link ImmutableMap#toImmutableMap(Function, Function)} from consumers of {@code
  ImmutableBiMap}.
  
  @throws UnsupportedOperationException always
  @deprecated Use {@link ImmutableBiMap#toImmutableBiMap}.