When updating a document with an invalid version I get the expected
json response with a 409 status and the error message.
The error with stack trace is also logged, either in console or
elasticsearch.log. Is this necessary? It doesn't really have any
other info that the json response doesn't have. Be great to remove
this message if poss.
Sorry to nitpick and I know its a debug message but some of our logs
are filled up with these messages.