@SuppressWarnings("unchecked") // reading data stored by writeObject
    private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
      stream.defaultReadObject();
      factory = (Supplier<? extends Collection<V>>) requireNonNull(stream.readObject());
      Map<K, Collection<V>> map = (Map<K, Collection<V>>) requireNonNull(stream.readObject());
      setMap(map);
    }

    void readEntries(ObjectInputStream in) throws IOException, ClassNotFoundException {
      while (true) {
        K key = (K) in.readObject();
        if (key == null) {
          break; // terminator
        }
        V value = (V) in.readObject();
        delegate.put(key, value);
      }
    }
  }

  /**

    ObjectInputStream in = new ObjectInputStream(new ByteArrayInputStream(serializedForm));

    ImmutableSet<?> deserialized = (ImmutableSet<?>) in.readObject();
    EnumSet<?> delegate = (EnumSet<?>) in.readObject();

    assertEquals(original, deserialized);
    assertTrue(delegate.remove(SomeEnum.A));
    assertTrue(deserialized.contains(SomeEnum.A));
  }

  @J2ktIncompatible

  }

  @Override
  @J2ktIncompatible // serialization
  Object writeReplace() {
    return new SerializedForm<>(this);
  }

  @J2ktIncompatible // java.io.ObjectInputStream
  private void readObject(ObjectInputStream stream) throws InvalidObjectException {
    throw new InvalidObjectException("Use SerializedForm");
  }

  // This class is never actually serialized directly, but we have to make the

  }

  @Override
  @J2ktIncompatible // serialization
  Object writeReplace() {
    return new SerializedForm<>(this);
  }

  @J2ktIncompatible // java.io.ObjectInputStream
  private void readObject(ObjectInputStream stream) throws InvalidObjectException {
    throw new InvalidObjectException("Use SerializedForm");
  }

  // This class is never actually serialized directly, but we have to make the