Question on HBase source code

I'm reading source code of hbase. When come to class org.apache.hadoop.hbase.zookeeper.ZooKeeperWatcher I find this class has private member *unassignedNodes* but I cannot find where nodes are added into the set.

To be figured out.

71   // set of unassigned nodes watched
72   private Set<String> unassignedNodes = new HashSet<String>();