gmaps.CircleOptions _circleOptionsFromCircle(Circle circle) {
  final populationOptions = gmaps.CircleOptions()
    ..strokeColor = _getCssColor(circle.strokeColor)
    ..strokeOpacity = _getCssOpacity(circle.strokeColor)
    ..strokeWeight = circle.strokeWidth
    ..fillColor = _getCssColor(circle.fillColor)
    ..fillOpacity = _getCssOpacity(circle.fillColor)
    ..center = gmaps.LatLng(circle.center.latitude, circle.center.longitude)
    ..radius = circle.radius
    ..visible = circle.visible   
    ..zIndex = circle.zIndex; <----- Missing
  return populationOptions;
}