function getId(payloadPiece, conf, path, fullPayload) {
    if (isWhat.isString(payloadPiece))
        return payloadPiece;
    if (isWhat.isPlainObject(payloadPiece)) {
        if ('id' in payloadPiece)
            return payloadPiece.id;
        var keys = Object.keys(payloadPiece);
        if (keys.length === 1)
            return keys[0];
    }
    return '';
}