The error reported is:
  undefined method `graph_db' for #<Neo4j::Server::CypherSession:0x3922b0a5>
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-core-6.0.4/lib/neo4j-embedded/label.rb:62:in `schema'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-core-6.0.4/lib/neo4j-embedded/label.rb:42:in `schema_query'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-core-6.0.4/lib/neo4j/transaction.rb:105:in `run'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-core-6.0.4/lib/neo4j-embedded/label.rb:41:in `schema_query'
org/jruby/RubyKernel.java:1858:in `tap'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-core-6.0.4/lib/neo4j-embedded/label.rb:40:in `schema_query'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-core-6.0.4/lib/neo4j-embedded/label.rb:9:in `constraints'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-core-6.0.4/lib/neo4j-embedded/label.rb:50:in `schema_index_operation'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-core-6.0.4/lib/neo4j-embedded/label.rb:17:in `constraint?'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-6.0.4/lib/neo4j/schema/operation.rb:83:in `exist?'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-6.0.4/lib/neo4j/schema/operation.rb:78:in `create!'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-6.0.4/lib/neo4j/active_node/labels/index.rb:68:in `schema_create_operation'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-6.0.4/lib/neo4j/active_node/labels/index.rb:36:in `constraint'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-core-6.0.4/lib/neo4j/session.rb:153:in `on_next_session_available'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-6.0.4/lib/neo4j/active_node/labels/index.rb:34:in `constraint'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-6.0.4/lib/neo4j/active_node/id_property.rb:144:in `id_property'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-core-6.0.4/lib/neo4j/session.rb:153:in `on_next_session_available'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-6.0.4/lib/neo4j/active_node/id_property.rb:141:in `id_property'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-6.0.4/lib/neo4j/active_node.rb:87:in `ActiveNode'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-core-6.0.4/lib/neo4j/session.rb:156:in `on_next_session_available'
org/jruby/RubyProc.java:281:in `call'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-core-6.0.4/lib/neo4j/session.rb:188:in `_notify_listeners'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-core-6.0.4/lib/neo4j-server/cypher_session.rb:19:in `initialize'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-core-6.0.4/lib/neo4j-server/cypher_session.rb:58:in `establish_session'
/opt/logstash/vendor/bundle/jruby/1.9/gems/neo4j-core-6.0.4/lib/neo4j-server/cypher_session.rb:52:in `open'
/opt/logstash/vendor/local_gems/7e8dcde4/logstash-output-dellgraph-0.0.5-java/lib/logstash/outputs/dellgraph.rb:17:in `register'
org/jruby/RubyArray.java:1613:in `each'
/opt/logstash/vendor/bundle/jruby/1.9/gems/logstash-core-2.1.1-java/lib/logstash/pipeline.rb:192:in `start_outputs'
/opt/logstash/vendor/bundle/jruby/1.9/gems/logstash-core-2.1.1-java/lib/logstash/pipeline.rb:102:in `run'
/opt/logstash/vendor/bundle/jruby/1.9/gems/logstash-core-2.1.1-java/lib/logstash/agent.rb:165:in `execute'
/opt/logstash/vendor/bundle/jruby/1.9/gems/logstash-core-2.1.1-java/lib/logstash/runner.rb:90:in `run'
org/jruby/RubyProc.java:281:in `call'
/opt/logstash/vendor/bundle/jruby/1.9/gems/logstash-core-2.1.1-java/lib/logstash/runner.rb:95:in `run'
org/jruby/RubyProc.java:281:in `call'
/opt/logstash/vendor/bundle/jruby/1.9/gems/stud-0.0.22/lib/stud/task.rb:24:in `initialize'