Context2D's font set to a default-constructed QFont when invalid font assigned

import QtQuick 2.0

Item {
    width: 500
    height: 400

    Canvas {
        anchors.fill: parent
        anchors.margins: 100

        onPaint: {
            var ctx = getContext("2d");
            ctx.reset();
            ctx.fillStyle = "#FF0000";
            ctx.fillText(ctx.font, 0, 10);

            ctx.font = "ffffff";
            ctx.fillText(ctx.font, 0, 20);
        }
    }
}