* multimap. Keys and values appear in the same order as in this multimap.
   */
  @Override
  @SuppressWarnings("unchecked") // a widening cast
  public ImmutableMap<K, Collection<V>> asMap() {
    return (ImmutableMap) map;
  }

  @Override
  Map<K, Collection<V>> createAsMap() {
    throw new AssertionError("should never be called");
  }

   * multimap. Keys and values appear in the same order as in this multimap.
   */
  @Override
  @SuppressWarnings("unchecked") // a widening cast
  public ImmutableMap<K, Collection<V>> asMap() {
    return (ImmutableMap) map;
  }

  @Override
  Map<K, Collection<V>> createAsMap() {
    throw new AssertionError("should never be called");
  }