igbinary/igbinary 3.1.1a1

on GitHub

Throw when an uninitialized php 7.4 typed property is included in the result of __sleep(),
instead of emitting a notice and attempting to represent the unset/uninitialized value as null (#258).
See https://bugs.php.net/bug.php?id=79002

Uninitialized properties without types (from __sleep) continue to cause igbinary to emit notices and are represented as null.