Garbd IP is not visible in wsrep_incoming_addresses status variable. Shows up only extra comma with empty string.
Testcase
1) start 2 node cluster.
2) start garbd daemon.

PXC: root@localhost ((none)) > show global status like '%wsrep_cluster_size%';
---------------------------+

---------------------------+

---------------------------+
1 row in set (0.00 sec)

PXC: root@localhost ((none)) > show global status like '%wsrep_incoming_addresses%';
------------------------------------------------------------------+

------------------------------------------------------------------+

------------------------------------------------------------------+
1 row in set (0.00 sec)
 

More over if we tune https://galeracluster.com/library/documentation/mysql-wsrep-options.html#wsrep-node-incoming-address variable other than AUTO the value is  shown blindly, i.e. 

wsrep_node_incoming_address=“10.202.236.68,10.202.236.8:3306,10.202.236.184”
PXC: root@localhost ((none)) > show global status like '%wsrep_incoming_addresses%';
-----------------------------------------------------------------------------------------------------------+

-----------------------------------------------------------------------------------------------------------+

-----------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
 

but even if I place a non-existent IP

wsrep_node_incoming_address=“10.202.236.68,10.202.236.8:3306,10.202.236.184,1.1.1.1:3306”

We see it printed in the status: 
PXC: root@localhost ((none)) > show global status like '%wsrep_incoming_addresses%';
-----------------------------------------------------------------------------------------------------------+

-----------------------------------------------------------------------------------------------------------+

-----------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
 

I think we have 3 potential solutions: 

• add wsrep_node_address variable to garbd daemon

• remove the empty value from wsrep_incoming_addresses

• grab the IP when garbd is connecting and report it correctly in wsrep_incoming_addresses