gremlin> graph = GraphFactory.open('conf/hadoop-graph/read-cql-standalone-cluster.properties')
==>hadoopgraph[cqlinputformat->nulloutputformat]
gremlin> g = graph.traversal().withComputer(SparkGraphComputer)
==>graphtraversalsource[hadoopgraph[cqlinputformat->nulloutputformat], sparkgraphcomputer]
gremlin> g.V().has('title','Plant').count()
11:09:18 WARN  org.apache.tinkerpop.gremlin.spark.process.computer.SparkGraphComputer  - class org.apache.hadoop.mapreduce.lib.output.NullOutputFormat does not implement PersistResultGraphAware and thus, persistence options are unknown -- assuming all options are possible
11:09:20 WARN  org.apache.spark.util.Utils  - Your hostname, ip-xx-xx-xx-xx resolves to a loopback address: 127.0.0.1; using xx.xx.xx.xx instead (on interface ens5)
11:09:20 WARN  org.apache.spark.util.Utils  - Set SPARK_LOCAL_IP if you need to bind to another address
11:10:25 ERROR org.apache.spark.scheduler.cluster.StandaloneSchedulerBackend  - Application has been killed. Reason: All masters are unresponsive! Giving up.
11:10:25 WARN  org.apache.spark.scheduler.cluster.StandaloneSchedulerBackend  - Application ID is not initialized yet.
11:10:25 WARN  org.apache.spark.deploy.client.StandaloneAppClient$ClientEndpoint  - Drop UnregisterApplication(null) because has not yet connected to master
11:10:25 WARN  org.apache.spark.metrics.MetricsSystem  - Stopping a MetricsSystem that is not running
11:10:26 ERROR org.apache.spark.SparkContext  - Error initializing SparkContext.
java.lang.NullPointerException
at org.apache.spark.SparkContext.<init>(SparkContext.scala:560)
at org.apache.spark.SparkContext$.getOrCreate(SparkContext.scala:2520)
at org.apache.spark.SparkContext.getOrCreate(SparkContext.scala)
at org.apache.tinkerpop.gremlin.spark.structure.Spark.create(Spark.java:52)
at org.apache.tinkerpop.gremlin.spark.structure.Spark.create(Spark.java:60)
at org.apache.tinkerpop.gremlin.spark.process.computer.SparkGraphComputer.lambda$submitWithExecutor$1(SparkGraphComputer.java:313)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
11:10:26 ERROR org.apache.spark.scheduler.AsyncEventQueue  - Listener AppStatusListener threw an exception
java.lang.NullPointerException
at org.apache.spark.status.AppStatusListener.onApplicationEnd(AppStatusListener.scala:157)
at org.apache.spark.scheduler.SparkListenerBus$class.doPostEvent(SparkListenerBus.scala:57)
at org.apache.spark.scheduler.AsyncEventQueue.doPostEvent(AsyncEventQueue.scala:37)
at org.apache.spark.scheduler.AsyncEventQueue.doPostEvent(AsyncEventQueue.scala:37)
at org.apache.spark.util.ListenerBus$class.postToAll(ListenerBus.scala:91)
at org.apache.spark.scheduler.AsyncEventQueue.org$apache$spark$scheduler$AsyncEventQueue$$super$postToAll(AsyncEventQueue.scala:92)
at org.apache.spark.scheduler.AsyncEventQueue$$anonfun$org$apache$spark$scheduler$AsyncEventQueue$$dispatch$1.apply$mcJ$sp(AsyncEventQueue.scala:92)
at org.apache.spark.scheduler.AsyncEventQueue$$anonfun$org$apache$spark$scheduler$AsyncEventQueue$$dispatch$1.apply(AsyncEventQueue.scala:87)
at org.apache.spark.scheduler.AsyncEventQueue$$anonfun$org$apache$spark$scheduler$AsyncEventQueue$$dispatch$1.apply(AsyncEventQueue.scala:87)
at scala.util.DynamicVariable.withValue(DynamicVariable.scala:58)
at org.apache.spark.scheduler.AsyncEventQueue.org$apache$spark$scheduler$AsyncEventQueue$$dispatch(AsyncEventQueue.scala:87)
at org.apache.spark.scheduler.AsyncEventQueue$$anon$1$$anonfun$run$1.apply$mcV$sp(AsyncEventQueue.scala:83)
at org.apache.spark.util.Utils$.tryOrStopSparkContext(Utils.scala:1302)
at org.apache.spark.scheduler.AsyncEventQueue$$anon$1.run(AsyncEventQueue.scala:82)
java.lang.NullPointerException
Type ':help' or ':h' for help.
Display stack trace? [yN]

Hadoop: 3.3.0

Spark: 2.2.2

Scala: 2.11.2

Janusgraph: 0.5.2

Referred the below documentation for configuration files: 

https://docs.janusgraph.org/advanced-topics/hadoop/ 

Thanks & Regards,

Vinayak