note 123247 rejected from datetime.format by cmb

Note Submitter: fabian dot picone at gmail dot com ---- This doc has something that does not match. The description of the method is "public string DateTimeImmutable::format ( string $format )". But the return value is documented as "Returns the formatted date string on success or FALSE on failure." . What is correct now, is the return a string or mixed? My tests showed up to result in string, could not break it to receive bool. So is this internally casted to string? Then you should adapt the return documentation.