cesium PolylineCollection 修改矩阵之后内容不显示

帮忙看下这段代码，为什么加上 polylines.modelMatrix =m; 之后线条就不会显示了

var polylines = new Cesium.PolylineCollection();
      polylines.add({
        positions: Cesium.Cartesian3.fromDegreesArrayHeights([
          110.254715, 22.871616, 959.058, 110.264715, 22.881616, 1024,
        ]),
        width: 10,
        material: Cesium.Material.fromType("Color", {
          color: Cesium.Color.BLUE,
        }),
      });
      polylines.add({
        positions: Cesium.Cartesian3.fromDegreesArrayHeights([
          110.254715, 22.871616, 959.058, 110.244715, 22.861616, 1032,
        ]),
        width: 4,
        material: Cesium.Material.fromType("Color", {
          color: Cesium.Color.RED,
        }),
      });
      var position = Cesium.Cartesian3.fromDegrees(
        110.254715,
        22.871616,
        959.058
      );
      var heading = Cesium.Math.toRadians(30);
      var pitch = Cesium.Math.toRadians(20);
      var roll = Cesium.Math.toRadians(10);
      var headingPitchRoll = new Cesium.HeadingPitchRoll(heading, pitch, roll);
      //var m =Cesium.Transforms.eastNorthUpToFixedFrame(position);
      var m = Cesium.Transforms.headingPitchRollToFixedFrame(
        position,
        headingPitchRoll,
        Cesium.Ellipsoid.WGS84,
        Cesium.Transforms.eastNorthUpToFixedFrame,
        new Cesium.Matrix4()
      );
      console.log(m);

      //polylines.modelMatrix =m;

      viewer.scene.primitives.add(polylines);

显示效果

你先看看m是不是null