docs: @Nullable
    public static String checkFileName (@Nullable final String sFilename)
    {
      if (sFilename != null && sFilename.indexOf ('\u0000') != -1)
      {
        throw new InvalidFileNameException (sFilename,
                                            "Invalid filename: " + StringHelper.replaceAll (sFilename, "\u0000", "\\0"));
      }
      return sFilename;
    }