I want to display a cropped image, but it doesn't work.

This is what I do:

var node = new umbraco.MacroEngines.DynamicNode(
ConfigurationManager.AppSettings["nodeID_News"].AsInt()
);

foreach (dynamic newsNode in node.Children()) {
    if (newsNode.HasValue("image")) {
        var imageUrl = newsNode.GetCropUrl("image", "newsOverview");
        <img src="@imageUrl">
    }
}

newsNode.image has a value, because I see the <img> tag getting rendered. And when I put a watch on newsNode.image, it shows me the following:

{
  "focalPoint": {
    "left": 0.5,
    "top": 0.5
  },
  "src": "/media/1007/nieuws.jpg",
  "crops": [
    {
      "alias": "newsOverview",
      "width": 307,
      "height": 261
    }
  ]
}

So there is a crop and a media item available. But still, GetCropUrl returns a {}

What am I doing wrong here?