Parameter kid appears in header even if not specified by the node

[telperion]

When generating a JWT with this node, the kid parameter is always included in the JOSE header even if that field is blank (it is set to the empty string). The presence of kid is causing some downstream APIs to refuse the token - which, admittedly, is probably their fault, but I'm hoping it's less friction to tidy up the token being produced.

                jwt.sign(msg[node.signvar],
                        node.secret,
                        {algorithm: node.alg, expiresIn: node.exp, keyid: node.jwkkid || null}, function (err, token) {