@NonNull
    public static <T> T checkNotNull(@Nullable T arg) {
        return checkNotNull(arg, "Argument must not be null");
    }
Deletes the contents of {@code dir}. Throws an IOException if any file
could not be deleted, or if {@code dir} is not a readable directory.
VideoSqlLite/src/main/java/com/yc/videosqllite/disk/DiskUtils.java