Description:
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When unserialising DateInterval, boolean fields are stored as integers.

http://3v4l.org/RkMGa

Test script:
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$interval = \DateInterval::createFromDateString('+1 month');
var_dump($interval->days === false);
var_dump(unserialize(serialize($interval))->days === false);

Expected result:
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bool(true)
bool(true)

Actual result:
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bool(true)
bool(false)