public boolean hasStaticMember(String instanceId) {
        if (instanceId == null) return false;
        return staticMembers.containsKey(instanceId);
    }
Returns true if the static member exists.

@param instanceId The instance id.

@return A boolean indicating whether the member exists or not.
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/modern/consumer/ConsumerGroup.java