code: public static <T> Optional<T> of(T value) {
      return new Optional<>(Objects.requireNonNull(value));
    }
docs: Returns an {@code Optional} with the specified present non-null value.
  @param <T> the class of the value
  @param value the value to be present, which must be non-null
  @return an {@code Optional} with the value present
  @throws NullPointerException if value is null