[FLINK-8065] Extend exception message if QS client is already shut down

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 1.4.0
• Component/s: Runtime / Queryable State
• Assignee: Kostas Kloudas
• Reporter: Chesnay Schepler
• Created: 13/Nov/17 15:58
• Updated: 17/Nov/17 10:09
• Resolved: 17/Nov/17 10:09

Description

Calling QueryableStateClient#getKvState after shutting it down leads to this rather short exception message:

Caused by: java.lang.IllegalStateException: Shut down
	at org.apache.flink.queryablestate.network.Client.sendRequest(Client.java:136)
	at org.apache.flink.queryablestate.client.QueryableStateClient.getKvState(QueryableStateClient.java:251)

We can extend this just a little bit.