docs: public static byte[] toBytes(String hexString) {
        if (hexString == null || hexString.length() % 2 != 0) {
           throw new RuntimeException("Input string must contain an even number of characters");
        }
        char[] hex = hexString.toCharArray();
        int length = hex.length / 2;
        byte[] raw = new byte[length];
        for (int i = 0; i < length; i++) {
           int high = Character.digit(hex[i * 2], 16);
           int low = Character.digit(hex[i * 2 + 1], 16);
           int value = (high << 4) | low;
           if (value > 127)
              value -= 256;
           raw[i] = (byte) value;
        }
        return raw;
     }