private static void maybeUpdateServerAssignors(
        Map<String, Integer> serverAssignorCount,
        ConsumerGroupMember oldMember,
        ConsumerGroupMember newMember
    ) {
        if (oldMember != null) {
            oldMember.serverAssignorName().ifPresent(name ->
                serverAssignorCount.compute(name, Utils::decValue)
            );
        }
        if (newMember != null) {
            newMember.serverAssignorName().ifPresent(name ->
                serverAssignorCount.compute(name, Utils::incValue)
            );
        }
    }
Updates the server assignors count.

@param serverAssignorCount   The count to update.
@param oldMember             The old member.
@param newMember             The new member.
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/modern/consumer/ConsumerGroup.java