Bug introduced in 6.0. This is the only unprotected d_ptr I could find.
[ChangeLog][QtCore][QMetaType] Fixed a bug that would cause
QMetaType::compare() and QVariant::compare() to crash on invalid meta
types and variants.
Pick-to: 6.2 6.3
Fixes: QTBUG-99960
Change-Id: I0e5f6bec596a4a78bd3bfffd16cb1f7b2d146688
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>