A customer reported this being logged every 5 seconds:
It looks like one of the connection handler's is returning a list containing a null ClientConnection. The only connection handlers enabled were the LDAP Connection Handler, Administration Connector, and the JMX Connection Handler.
(I note there were various JMX connection bugs in 2.6.0 which may be the root cause of the nulls.)
A consequence of the bug is that the idling thread fails and will never idle out any connections after the null.
I don't think there's much we can do here except log the connection handler name and skip if we get a null ClientConnection.