Rounded Rectangle, set CornerRounding

GoJS
1

How can i set the cornerRounding parameter, when i am using a roundedRectangle ?

I have tried

_$(go.Shape, "RoundedRectangle", {
        fill: Constants.canvasStyle.colors.tooltipBackground,
        cornerRounding: 1
    })

but this gives me a console error

2

There is no cornerRounding property. Set parameter1 instead. GoJS Shapes -- Northwoods Software