QML Plugin Example shows a blank window

Can't see anything when launching examples/qml/tutorials/extending-qml/chapter6-plugins

To reproduce:

git clone --depth=1 https://code.qt.io/qt/qtdeclarative.git
cd qtdeclarative
git fetch --tags
git checkout v6.8.3
cd examples/qml/tutorials/extending-qml/chapter6-plugins
cmake .
make -j
./chapter6-plugins

Shows a white window instead of a pie chart.

Something is wrong with the QML code in examples/qml/tutorials/extending-qml/chapter6-plugins/App.qml. When setting parent to the PieSlices, they show up.