public static String joinReason(JoinGroupRequestData request) {
        String joinReason = request.reason();
        if (joinReason == null || joinReason.isEmpty()) {
            joinReason = "not provided";
        }
        return joinReason;
    }
Get the client's join reason.

@param request The JoinGroupRequest.

@return The join reason.
clients/src/main/java/org/apache/kafka/common/requests/JoinGroupRequest.java