Open layer 3 (3.8.2) How to set a blank Basemap?

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I want to add a blank (empty) base map option to the set of radio button .

here is how a part of my code looks.

// MapQuest streets new ol.layer.Tile({ title: 'Street Map', group: "background", source: new ol.source.MapQuest({layer: 'osm'}) }), // MapQuest imagery new ol.layer.Tile({ title: 'Aerial Imagery', group: "background", visible: false, source: new ol.source.MapQuest({layer: 'sat'}) }), // MapQuest hybrid (uses a layer group) new ol.layer.Group({ title: 'Imagery with Streets', group: "background", visible: false, layers: [ new ol.layer.Tile({ source: new ol.source.MapQuest({layer: 'sat'}) }), new ol.layer.Tile({ source: new ol.source.MapQuest({layer: 'hyb'}) }) ] }),

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