private void throwIfMemberDoesNotUseClassicProtocol(ConsumerGroupMember member) {
        if (!member.useClassicProtocol()) {
            throw new UnknownMemberIdException(
                String.format("Member %s does not use the classic protocol.", member.memberId())
            );
        }
    }
Validates if the consumer group member uses the classic protocol.

@param member The ConsumerGroupMember.
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/GroupMetadataManager.java