[移动开发]lPointerException: null cannot be cast to non-null type android.util.SparseArray＜android.view.View?＞

kotlin的报错提示：
java.lang.NullPointerException: null cannot be cast to non-null type android.util.SparseArray<android.view.View?>

报错信息可能是：null不能转换到非null类型SparseArray<android.view.View?>
先看看ViewHolder.kt

object ViewHolder {
    operator fun <T : View?> get(view: View, id: Int): T? {
        //j节省内存，提高性能，使用SparseArray
        var viewHolder = view.tag as SparseArray<View?>

        if (viewHolder == null) {
            viewHolder = SparseArray()

            view.tag = viewHolder
        }
        var childView = viewHolder[id]
        if (childView == null) {
            childView = view.findViewById(id)
            viewHolder.put(id, childView)
        }
        return childView as T?
    }
}

这代码中：

var viewHolder = view.tag as SparseArray<View?>

改为：

var viewHolder = view.tag as? SparseArray<View?>