WebTiledLayer with fullExtent doesn't work

[ColinDoig]

Tiles are not displayed if fullExtent is specified like this: 

var cycleMap = new WebTiledLayer("https://${subDomain}.tile.thunderforest.com/cycle/${level}/${col}/${row}.png", {
"copyright": 'Maps &copy; <a href="http://www.thunderforest.com">Thunderforest</a>, Data &copy; <a href="http://www.openstreetmap.org/copyright">OpenStreetMap contributors</a>',
    "fullExtent": new Extent(-179, 0, 179, 60),
    "id": "OpenCycleMap",
    "subDomains": ["a", "b", "c"]
});

See here : https://codepen.io/captain-igloo/pen/VwKwyOW?editors=100