DatePeriod class does not have the serialization/unserialization logic implemented. Therefore, when unserialized instance is used, script crashes.
unserialize() wents fine as well, but when I call foreach() on unserialized instance, the script crashes.
PHP crashes on the "unserialize" line.
Log: - Added a test case for #53437.
The fix here was to break backwards compatibility with existing classes that extend DatePeriod? It's difficult to believe that DateTime can be extended with additional properties, but that DatePeriod cannot.