无法将Firebase存储数据转换为UIImage

Question

我正在尝试从Firebase Storage下载图像并将其显示在我的iOS应用中。我有以下代码：

func getSponsorImages() {
    guard let name = self.name, let city = self.city else { return }
    let refString = "cities/\(city)/sponsors/\(name)/photos"
    ref.child(refString).observeSingleEvent(of: .value, with: { (snapshot) in
        if let snapshots = snapshot.children.allObjects as? [DataSnapshot], snapshots.count != 0 {
            for snap in snapshots {
                let imageRef = storageRef.child("cities/\(city)/\(name)/\(snap.value!)")
                imageRef.getData(maxSize: 50*1024*1024) { data, error in
                    if let error = error {
                        print("Error getting image: \(error.localizedDescription)")
                    } else {
                        guard let photoData = data else { return }
                        guard let photo = UIImage(data: photoData) else { return }
                        self.photos.append(photo!)
                    }
                }
            }
        }

    })
}

正在返回数据，并且没有引发任何错误，但是当我尝试从Data创建UIImage时，它崩溃了。有谁知道为什么它返回无效数据？我还确保正确设置了Firebase规则。