"invalid nullptr parameter" when running Qt Quick Controls - Contact List example

When I try to run this example against the Qt 5.15.1 kit for MSVC 2019 or Qt 6.0 for mingw, I get these warnings:

qt.core.qobject.connect: QObject::connect(QWindow, QQuickStyleItemTextField): invalid nullptr parameter
qt.core.qobject.connect: QObject::connect(QWindow, QQuickStyleItemTextField): invalid nullptr parameter
qt.core.qobject.connect: QObject::connect(QWindow, QQuickStyleItemTextField): invalid nullptr parameter
qt.core.qobject.connect: QObject::connect(QWindow, QQuickStyleItemTextField): invalid nullptr parameter

I think the example is missing the style because of these warnings.