@NonNull
    public static <T> T checkNotNull(@Nullable T arg, @NonNull String message) {
        if (arg == null) {
            throw new NullPointerException(message);
        }
        return arg;
    }
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