Construction from nullptr isn't, because it's using the QPointer(T*)
constructor, which cannot be constexpr.
Pick-to: 6.5
Change-Id: I19129a0fca5873e83d20351a909a7994399bfcce
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 8b661846257670a1b8ef6b33593778c0f086c5e3)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>