LifeCycleHook - graph snapshots onShutDown method

onShutDown: { ctx ->
        def outputFile = '/tmp/snapshot.json'
        ctx.logger.info("Gremlin Server is shutting down. Writing out the graph to ${outputFile}...")
        try {
            graph.io(org.apache.tinkerpop.gremlin.structure.io.IoCore.graphson()).writeGraph(outputFile)
            ctx.logger.info("Target graph written to file: ${outputFile}")
        } catch (Exception e) {
            ctx.logger.error("Failed to write target graph to ${outputFile}", e)
        }
    }

onShutDown: { ctx ->
        def outputFile = '/tmp/snapshot.json'
        ctx.logger.info("Gremlin Server is shutting down. Writing out the graph to ${outputFile}...")
        try {
            graph.io(org.apache.tinkerpop.gremlin.structure.io.IoCore.graphson()).writeGraph(outputFile)
            ctx.logger.info("Target graph written to file: ${outputFile}")
        } catch (Exception e) {
            ctx.logger.error("Failed to write target graph to ${outputFile}", e)
        }
    }

08:55:41 INFO org.apache.tinkerpop.gremlin.server.GremlinServer.lambda$stop$6 - Executing shutdown LifeCycleHook
08:55:41 INFO org.codehaus.groovy.vmplugin.v8.IndyInterface.fromCache - Gremlin Server is shutting down. Writing out the graph to /tmp/snapshot.json...
08:55:41 ERROR org.codehaus.groovy.vmplugin.v8.IndyInterface.fromCache - Failed to write target graph to /tmp/snapshot.json
java.lang.IllegalStateException: Graph has been closed
at org.janusgraph.graphdb.tinkerpop.JanusGraphBlueprintsGraph.getAutoStartTx(JanusGraphBlueprintsGraph.java:76) ~[janusgraph-core-1.1.0.jar:?]
...

08:55:43 INFO org.apache.tinkerpop.gremlin.server.GremlinServer.lambda$stop$7 - Closed GraphTraversalSource instance [g]
08:55:43 INFO org.apache.tinkerpop.gremlin.server.GremlinServer.lambda$stop$8 - Closed Graph instance [graph]