Missing Bing Image preview in MapControls.LayerSwitcherImageControl

[1Map]

Describe the bug
The image preview is missing in MapControls.LayerSwitcherImageControl for a Bing Maps Source.

To Reproduce
Add Bing Layer with Sources.SourceBingMaps and also add MapControls.LayerSwitcherImageControl. Preview image not showing.

Expected behavior
Suppose to see preview image

[d-koppenhagen]

I added some documentation. Please define the imagerySet on ol-source-bing. This should fix your issue. I added this example also to the MapControls demo.