* contained references are {@linkplain Object#equals equal} to each other or both are absent.
   * Note that {@code Optional} instances of differing parameterized types can be equal.
   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> no differences.
   */
  @Override
  public abstract boolean equals(@CheckForNull Object object);

  /**

   * contained references are {@linkplain Object#equals equal} to each other or both are absent.
   * Note that {@code Optional} instances of differing parameterized types can be equal.
   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> no differences.
   */
  @Override
  public abstract boolean equals(@CheckForNull Object object);

  /**