QML fails to run benchmarks in qmlbench's v8bench directory

ulf@fant:~/dev/qmlbench/benchmarks/manual/v8bench$ ~/dev/build-qmlbench-Desktop_Qt_5_12_7_GCC_64bit-Profile/src/qmlbench v8-DeltaBlue.qml 
ID:          
OS:          Debian GNU/Linux 10 (buster)
QPA:         xcb
GL_VENDOR:   X.Org
GL_RENDERER: Radeon RX 570 Series (POLARIS10, DRM 3.27.0, 4.19.0-14-amd64, LLVM 7.0.1)
GL_VERSION:  4.5 (Compatibility Profile) Mesa 18.3.6
running: /home/ulf/dev/qmlbench/benchmarks/manual/v8bench/v8-DeltaBlue.qml
    244 frames
qrc:/3rdparty/v8-bench.js:73: TypeError: Type error
qrc:/V8Benchmark.qml:63: TypeError: Cannot read property 'benchmarks' of undefined
qrc:/V8Benchmark.qml:81: TypeError: Value is undefined and could not be converted to an object
qrc:/V8Benchmark.qml:81: TypeError: Value is undefined and could not be converted to an object
qrc:/V8Benchmark.qml:81: TypeError: Value is undefined and could not be converted to an object
[...]