if (escaper instanceof UnicodeEscaper) {
      return (UnicodeEscaper) escaper;
    } else if (escaper instanceof CharEscaper) {
      return wrap((CharEscaper) escaper);
    }
    // In practice this shouldn't happen because it would be very odd not to
    // extend either CharEscaper or UnicodeEscaper for non-trivial cases.
    throw new IllegalArgumentException(