preloadScene回调sceneAsset是null

[hubluesky (hublueskyfool)]

director.preloadScene在加载完成回调后，sceneAsset是null。error也是null。

               let progressScale: number = 1 / this.taskCount / 100;
                director.preloadScene(task.url, (progressCount, totalCount) => {
                    let progress = progressCount / totalCount;
                    this.callProgressChanged(this.completedCount / this.taskCount + progress * progressScale);
                }, (error, asset) => {
                    onCompleted(task, error, asset);
                });