QML type registration emits "qt6quick_metatypes.json: illegal value"

Fresh Qt 6.2 checkout from July, 2nd.

I configure Qt like so

configure -no-warnings-are-errors -nomake examples -prefix C:\Users\alportal\dev\qt6_desktop\qtbase -debug-and-release

During the build, I get these error messages (but the build continues)

[4537/10634] Automatic QML type registration for target LabsAnimation
Error 5 while parsing C:/Users/alportal/dev/qt6_desktop/qtbase/lib/metatypes/qt6quick_metatypes.json: illegal value
[4541/10634] Automatic QML type registration for target QuickParticlesPrivate
Error 5 while parsing C:/Users/alportal/dev/qt6_desktop/qtbase/lib/metatypes/qt6quick_metatypes.json: illegal value
[4553/10634] Automatic QML type registration for target LabsWavefrontMesh
Error 5 while parsing C:/Users/alportal/dev/qt6_desktop/qtbase/lib/metatypes/qt6quick_metatypes.json: illegal value
[4555/10634] Automatic QML type registration for target LabsSharedImage
Error 5 while parsing C:/Users/alportal/dev/qt6_desktop/qtbase/lib/metatypes/qt6quick_metatypes.json: illegal value

qtbase/lib/metatypes/qt6quick_metatypes.json has a file size of 0