static void quoteToPrintWriter(S s, PrintWriter out) {
  if (s == null) { out.print("null"); ret; }
  out.print('"');
  int l = s.length();
  for (int i = 0; i < l; i++) {
    char c = s.charAt(i);
    if (c == '\\' || c == '"') {
      out.print('\\'); out.print(c);
    } else if (c == '\r')
      out.print("\\r");
    else if (c == '\n')
      out.print("\\n");
    else if (c == '\0')
      out.print("\\0");
    else
      out.print(c);
  }
  out.print('"');
}