private static void verifyByteStringRoundtripsAsValidUtf8(byte[] byteStr) {
        String asStr   = fromUtf8Bytes(byteStr); // Replaces bad chars with a placeholder
        byte[] asBytes = toUtf8Bytes(asStr);
        if (!Arrays.equals(byteStr, asBytes)) {
            throw new IllegalArgumentException("Key ID is not valid normalized UTF-8");
        }
    }
@return the raw backing byte array. <strong>Must therefore not be mutated.</strong>
security-utils/src/main/java/com/yahoo/security/KeyId.java