obj model loading issue

loader.ts

  private loadAssets(){
    console.log("loading assets");
    this._assetManager=new AssetsManager(this._Scene);
    let meshTask=this._assetManager.addMeshTask("gemTask","gem","../Assets/","diamond.obj");
    meshTask.onSuccess=(task:MeshAssetTask)=>{
      console.log("load success");
      task.loadedMeshes[0].position=Vector3.Zero();
    }
    meshTask.onError=(task,message,exception)=>{
      console.log(message,exception);
    }
    this._assetManager.onFinish=(tasks)=>{
      console.log("loading finished");
      this.runEngine();
    }