Corridor renders from Primitive API but not Entity API

From #4326

This corridor renders:

var viewer = new Cesium.Viewer('cesiumContainer');
var scene = viewer.scene;

var redCorridorInstance = new Cesium.GeometryInstance({
    geometry: new Cesium.CorridorGeometry({
        positions : Cesium.Cartesian3.fromDegreesArray([
            -16.41549000000001,28.44423000000001,
            -16.41549000000001,28.44423000000001,
            -16.41505000000001,28.44430000000001,
            -16.41507000000001,28.44430000000001,
            -16.41473000000001,28.44460000000001,
            -16.41429000000001,28.44452000000001,
            -16.41430000000001,28.44453000000001,
            -16.41428000000001,28.44452000000001,
            -16.41416000000001,28.44434000000001,
            -16.41415000000001,28.44434000000001,
            -16.41397000000001,28.44408000000001
        ]),
        width : 1,
        vertexFormat : Cesium.PerInstanceColorAppearance.VERTEX_FORMAT
    }),
    attributes : {
        color : Cesium.ColorGeometryInstanceAttribute.fromColor(new Cesium.Color(1.0, 0.0, 0.0, 0.5))
    }
});

var primitive = scene.groundPrimitives.add(new Cesium.GroundPrimitive({
    geometryInstances: [redCorridorInstance],
    appearance: new Cesium.PerInstanceColorAppearance({
        closed: true
    })
}));

scene.camera.setView({
    destination: Cesium.Cartesian3.fromDegrees(-16.41549000000001, 28.44423000000001, 100)
});

But this one doesn't

var viewer = new Cesium.Viewer('cesiumContainer');

var redCorridor = viewer.entities.add({
    name : 'Red corridor on surface with rounded corners and outline',
    corridor : {
        positions : Cesium.Cartesian3.fromDegreesArray([
            -16.41549000000001,28.44423000000001,
            -16.41549000000001,28.44423000000001,
            -16.41505000000001,28.44430000000001,
            -16.41507000000001,28.44430000000001,
            -16.41473000000001,28.44460000000001,
            -16.41429000000001,28.44452000000001,
            -16.41430000000001,28.44453000000001,
            -16.41428000000001,28.44452000000001,
            -16.41416000000001,28.44434000000001,
            -16.41415000000001,28.44434000000001,
            -16.41397000000001,28.44408000000001
        ]),
        width : 1,
        material : Cesium.Color.RED.withAlpha(0.5),
        outline : true,
        outlineColor : Cesium.Color.RED
    }
});

viewer.zoomTo(viewer.entities);