I don't know why std::shared_ptr allows this, but why not.
[ChangeLog][Important Behavior Changes] QSharedPointer objects will now
call custom deleters even when the pointer being tracked was null. This
behavior is the same as std::shared_ptr.
Fixes: QTBUG-85285
Pick-to: 5.15
Change-Id: I24006db8360041f598c5fffd161c260df0313b55
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>