Can't verify JWT with jose4j with header at null in a CompactSerialization form

Question

I'm trying to play with jose4j and for example I tried to verify JsonWebSignature without setting the first part of CompactSerialization (as we use unprotected header).

It returns me

org.jose4j.lang.JoseException: Parsing error: org.jose4j.json.internal.json_simple.parser.ParseException: Unexpected character (�) at position 0.

Do you have any idea to permit that?

Thanks

Edit
Code is:

JsonWebSignature jws = new JsonWebSignature();

LicenseKeystore lk = new LicenseKeystore();

jws.setAlgorithmConstraints(new AlgorithmConstraints(ConstraintType.PERMIT, lk.KS_ALG));

JsonCanonicalizer jc = new JsonCanonicalizer(jsonSigned);

jws.setCompactSerialization(new Base64Url().base64UrlEncodeUtf8ByteRepresentation(null) + "." +
    new Base64Url().base64UrlEncodeUtf8ByteRepresentation(jc.getEncodedString()) + "." +
    cs.getSignature());

jws.setKey(lk.getPublicKey());

try {
    return jws.verifySignature();
} catch (InvalidAlgorithmException e) {
    return false;
}

JWS is in the type of .[payload].[signature]