qmlcachgen assert when assign value to a custom list

C:\WINDOWS\system32\cmd.exe /C "cd /D C:\Users\semla\work\qt\build_qtgrpc\qtgrpc\tests\auto\protobufqml\messagelists && C:\Qt\Tools\CMake_64\bin\cmake.exe -E make_directory C:/Users/semla/work/qt/build_qtgrpc/qtgrpc/tests/auto/protobufqml/messagelists/.rcc/qmlcache/tst_protobuf_repeated_qml_qml && C:\Users\semla\work\qt\build_qtgrpc\.qt\bin\qt_setup_tool_path.bat C:/Users/semla/work/qt/build_qtgrpc/qtbase/bin/qmlcachegen.exe --bare --resource-path /qt/qml/QmlTestUri/qml/tst_repeated.qml -I C:/Users/semla/work/qt/build_qtgrpc/qtgrpc/tests/auto/protobufqml/messagelists -I C:/Users/semla/work/qt/build_qtgrpc/qtbase/qml -i C:/Users/semla/work/qt/build_qtgrpc/qtgrpc/tests/auto/protobufqml/messagelists/QmlTestUri/qmldir --resource C:/Users/semla/work/qt/build_qtgrpc/qtgrpc/tests/auto/protobufqml/messagelists/.qt/rcc/qmake_QmlTestUri.qrc --resource C:/Users/semla/work/qt/build_qtgrpc/qtgrpc/tests/auto/protobufqml/messagelists/.qt/rcc/tst_protobuf_repeated_qml_raw_qml_0.qrc --resource C:/Users/semla/work/qt/build_qtgrpc/qtgrpc/tests/auto/protobufqml/messagelists/.qt/rcc/tst_protobuf_repeated_qml_raw_qml_0_extra_qmldirs.qrc --dump-aot-stats --module-id=QmlTestUri(tst_protobuf_repeated_qml) -o C:/Users/semla/work/qt/build_qtgrpc/qtgrpc/tests/auto/protobufqml/messagelists/.rcc/qmlcache/tst_protobuf_repeated_qml_qml/tst_repeated_qml.cpp C:/Users/semla/work/qt/qt5/qtgrpc/tests/auto/protobufqml/messagelists/qml/tst_repeated.qml"
ASSERT: "readIt->second.content.conversionResultType()" in file C:\Users\semla\work\qt\qt5\qtdeclarative\src\qmlcompiler\qqmljsoptimizations.cpp, line 135