private boolean isNotInGroup() {
        return state == MemberState.UNSUBSCRIBED ||
                state == MemberState.FENCED ||
                state == MemberState.FATAL ||
                state == MemberState.STALE;
    }
@return True if the consumer is not a member of the group.
clients/src/main/java/org/apache/kafka/clients/consumer/internals/ShareMembershipManager.java