Unable to get bulk loading working in BerkleyJE backend

[derMart]

Hey, we have the following JanusGraph setup:

• Version: 0.6.3
• Storage Backend: berkleyje
• Mixed Index Backend: lucene

We use this with JRuby, but this translates directly to Java code.
Problem is I am unable to get bulk loading working: https://docs.janusgraph.org/operations/bulk-loading/
Opening the instance as follows:

org.janusgraph.core.JanusGraphFactory.build
      .set("storage.backend","berkeleyje")
      .set("storage.directory", @db_folder)
      .set("storage.batch-loading","true") # this enables bulk loading, without this line query below executes as expected
      .set("allow_upgrade",false)
      .set("lock-mode","READ_UNCOMMITTED")
      .set("jvm_cache","50")
      .set("timestamp_provider","NANO")
      .set("index.search.backend","lucene")
      .set("index.search.directory","#{@db_folder}/index")
      .set("query.batch-property-prefetch","true")
      .set("query.fast-property","true")
      .set("query.force-index","false")
      .open()

but running a simple query such as:

db.traversal.v.has("nodetype", node_type).to_list()

is crashing because a transaction can't be opened:

org.janusgraph.graphdb.database.StandardJanusGraph.newTransaction(StandardJanusGraph.java:400): Could not start new transaction (Java::OrgJanusgraphCore::JanusGraphException)
	from org.janusgraph.graphdb.database.StandardJanusGraph$1.retrieveSchemaByName(StandardJanusGraph.java:423)
	from org.janusgraph.graphdb.database.cache.StandardSchemaCache.getSchemaId(StandardSchemaCache.java:111)
	from org.janusgraph.graphdb.transaction.StandardJanusGraphTx.getSchemaVertex(StandardJanusGraphTx.java:1033)
	from org.janusgraph.graphdb.transaction.StandardJanusGraphTx.getRelationType(StandardJanusGraphTx.java:1053)
	from org.janusgraph.graphdb.query.QueryUtil.getType(QueryUtil.java:87)
	from org.janusgraph.graphdb.query.QueryUtil.constraints2QNF(QueryUtil.java:183)
	from org.janusgraph.graphdb.query.graph.GraphCentricQueryBuilder.constructQueryWithoutProfile(GraphCentricQueryBuilder.java:272)
	from org.janusgraph.graphdb.tinkerpop.optimize.step.JanusGraphStep.buildGraphCentricQuery(JanusGraphStep.java:193)
	from org.janusgraph.graphdb.tinkerpop.optimize.step.JanusGraphStep.buildGlobalGraphCentricQuery(JanusGraphStep.java:163)
	from org.janusgraph.graphdb.tinkerpop.optimize.step.JanusGraphStep.buildGlobalGraphCentricQuery(JanusGraphStep.java:131)
	from org.janusgraph.graphdb.tinkerpop.optimize.step.JanusGraphStep.lambda$new$1(JanusGraphStep.java:87)
	from org.apache.tinkerpop.gremlin.process.traversal.step.map.GraphStep.processNextStart(GraphStep.java:158)
	from org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.hasNext(AbstractStep.java:150)
	from org.apache.tinkerpop.gremlin.process.traversal.util.DefaultTraversal.hasNext(DefaultTraversal.java:235)
	from org.jruby.dist/org.jruby.javasupport.ext.JavaUtil$Iterator.each(JavaUtil.java:113)

am I missing something to get bulk loading to work?

best