* Number value = first.or(0.5); // error
   * }</pre>
   *
   * <p>As a workaround, it is always safe to cast an {@code Optional<? extends T>} to {@code
   * Optional<T>}. Casting either of the above example {@code Optional} instances to {@code
   * Optional<Number>} (where {@code Number} is the desired output type) solves the problem:
   *
   * <pre>{@code

   * Number value = first.or(0.5); // error
   * }</pre>
   *
   * <p>As a workaround, it is always safe to cast an {@code Optional<? extends T>} to {@code
   * Optional<T>}. Casting either of the above example {@code Optional} instances to {@code
   * Optional<Number>} (where {@code Number} is the desired output type) solves the problem:
   *
   * <pre>{@code