What I am trying to do is to replace or change the geometry of a feature after it has been drawn. e.g.: I draw a line and after it has been drawn I modify the geometry with `Turf.js`, to make a buffer around the drawn line and display the buffered line(polygon) instead of the line.

```
var draw = new ol.interaction.Draw({
    source: vectorSource,
    type: 'LineString'
});

draw.on('drawend', function(e) {

    //Sending the LineString to a Turf function with a buffer value and getting a Polygon in return
    var bfc = bufferedFeatureCollection(100, e.feature);

    //Replacing the LineString geometry with a Polygon geometry
    e.feature.setGeometry(bfc[0].getGeometry());

    //Removes and terminates the draw action.... 
    map.removeInteraction(this);
});

```

Now from `console.log()`, I can see that the `feature.geometry` has been changed from `ol.geom.linestring` to `ol.geom.polygon`. But on the map I still see a line being displayed.

What am I doing wrong?