I use such an environment: 

For confirmed bugs, please report:

- Version:  JanusGraph 0.5, Spark 2.4.6

- Storage Backend: cassandra:3

- Mixed Index Backend: elasticsearch:6.6.0

- Steps to Reproduce: 

    

    1. Use janusgraph-docker project to start all services:

    

        ```shell

        docker-compose -f docker-compose-cql-es.yml up

        ```

   2. In my spark project code like this:

      ```scala

          val properties = path + "hadoop-graph/read-cql.properties"

          val propertiesConfiguration = new PropertiesConfiguration(properties)

          val graph = GraphFactory.open(propertiesConfiguration)

          val g = graph.traversal().withComputer(classOf[SparkGraphComputer])

          println(g.V().count().next())

      ```

### Stack Trace 

```

org.janusgraph.core.JanusGraphException: Could not execute operation due to backend exception

        at org.janusgraph.diskstorage.util.BackendOperation.execute(BackendOperation.java:56)

        at org.janusgraph.diskstorage.util.BackendOperation.execute(BackendOperation.java:158)

        at org.janusgraph.diskstorage.configuration.backend.KCVSConfiguration.get(KCVSConfiguration.java:94)

        at org.janusgraph.diskstorage.configuration.BasicConfiguration.isFrozen(BasicConfiguration.java:105)

        at org.janusgraph.diskstorage.configuration.builder.ReadConfigurationBuilder.buildGlobalConfiguration(ReadConfigurationBuilder.java:70)

        at org.janusgraph.graphdb.configuration.builder.GraphDatabaseConfigurationBuilder.build(GraphDatabaseConfigurationBuilder.java:53)

        at org.janusgraph.core.JanusGraphFactory.open(JanusGraphFactory.java:161)

        at org.janusgraph.core.JanusGraphFactory.open(JanusGraphFactory.java:132)

        at org.janusgraph.core.JanusGraphFactory.open(JanusGraphFactory.java:122)

        at org.janusgraph.hadoop.formats.util.input.current.JanusGraphHadoopSetupImpl.<init>(JanusGraphHadoopSetupImpl.java:58)

        at org.janusgraph.hadoop.formats.util.HadoopInputFormat.lambda$static$0(HadoopInputFormat.java:41)

        at org.janusgraph.hadoop.formats.util.HadoopInputFormat$RefCountedCloseable.acquire(HadoopInputFormat.java:94)

        at org.janusgraph.hadoop.formats.util.HadoopRecordReader.<init>(HadoopRecordReader.java:50)

        at org.janusgraph.hadoop.formats.util.HadoopInputFormat.createRecordReader(HadoopInputFormat.java:56)

        at org.apache.spark.rdd.NewHadoopRDD$$anon$1.liftedTree1$1(NewHadoopRDD.scala:197)

.....

Caused by: org.janusgraph.diskstorage.PermanentBackendException: Permanent exception while executing backend operation getConfiguration

        at org.janusgraph.diskstorage.util.BackendOperation.executeDirect(BackendOperation.java:81)

        at org.janusgraph.diskstorage.util.BackendOperation.execute(BackendOperation.java:54)

        ... 42 more

Caused by: java.lang.NoSuchMethodError: io.vavr.concurrent.Future.fromJavaFuture(Ljava/util/concurrent/ExecutorService;Ljava/util/concurrent/Future;)Lio/vavr/concurren

t/Future;

        at org.janusgraph.diskstorage.cql.CQLKeyColumnValueStore.getSlice(CQLKeyColumnValueStore.java:280)

        at org.janusgraph.diskstorage.configuration.backend.KCVSConfiguration$1.call(KCVSConfiguration.java:97)

        at org.janusgraph.diskstorage.configuration.backend.KCVSConfiguration$1.call(KCVSConfiguration.java:94)

        at org.janusgraph.diskstorage.util.BackendOperation.execute(BackendOperation.java:147)

        at org.janusgraph.diskstorage.util.BackendOperation$1.call(BackendOperation.java:161)

        at org.janusgraph.diskstorage.util.BackendOperation.executeDirect(BackendOperation.java:68)

        ... 43 more

```

I am pretty sure this method exists.  I don't know why this happens. Because I first use this database, maybe just some config I make wrong. 

So thank you for looking!!!