Cesium 运动实体消失的时候报错 Uncaught TypeError: Cannot read property ‘x‘ of undefined

{
    "id": "2129c05288d445708a601d5953be57ac",
    "name": "测试 001",
    "type": "004",
    "properties": {
        "status": "use"
    },
    "position": {
        "interpolationAlgorithm": "LAGRANGE",
        "interpolationDegree": 1,
        "epoch": "2022-09-10T00:00:00Z",
        "cartographicDegrees": [
            0,
            11,
            22,
            100,
            5000,
            33,
            55,
            200
        ]
    },
    "model": {
        "show": true,
        "gltf": "http://localhost:1024/earth/model/missile.glb",
        "scale": 10,
        "minimumPixelSize": 16
    },
    "label": {
        "fillColor": {
            "rgba": [
                233,
                150,
                122,
                255
            ]
        },
        "outlineWidth": 2,
        "verticalOrigin": "CENTER",
        "outlineColor": {
            "rgba": [
                0,
                0,
                0,
                255
            ]
        },
        "show": true,
        "horizontalOrigin": "LEFT",
        "scale": 0.5,
        "style": "FILL_AND_OUTLINE",
        "text": "测试",
        "pixelOffset": {
            "cartesian2": [
                5,
                -60
            ]
        },
        "font": "21pt Lucida Console"
    }
}

这里创建了一个运动实体测试 001

positions: new Cesium.CallbackProperty(function() {
                          try {
                            const userEntityExists = ds.entities.getById(userEntity.id);
                            const closestSatelliteExists = closestDataSource.entities.getById(closestSatellite.id);

                            if (userEntityExists && userEntityExists.position && closestSatelliteExists && closestSatelliteExists.position) {
                              return [userEntityExists.position.getValue(viewer.clock.currentTime), closestSatelliteExists.position.getValue(viewer.clock.currentTime)];
                            } else {
                              viewer.entities.removeById(lineID);
                              return null;
                            }
                          } catch (error) {
                            console.error(`An error occurred while creating the polyline for ${lineID}: `, error);
                            viewer.entities.removeById(lineID);
                            return null;
                          }
                        }, false),

这里使用了 Cesium.CallbackProperty 来获取 postion 创建实体测试 001 和卫星的连线,现在当测试 001 消失的时候会报错 Uncaught TypeError: Cannot read property ‘x‘ of undefined 这个要怎么处理呢