Imagery provider : how to remove/disable?

CesiumJS
1

Good morning,
It seems to have a default baselayer with cesiumJS(Bing). I would like to remove/disable any baselayer imagery provider. Could you tell me how to do?
Thanks a lot.

2

var viewer = new Cesium.Viewer(“cesiumContainer”, {
imageryProvider: false,
baseLayerPicker: false,
});