JanusGraph BulkLoad reports NoSuchElement Error, nodes loaded but no edges - gremlin

Question

I am exporing ways of loading csv in JanusGraph. I tried the grateful-dead example given by the official document and it worked just fine. Approach as follows:
hadoop-load-csv.properties
gremlin.graph=org.apache.tinkerpop.gremlin.hadoop.structure.HadoopGraph
gremlin.hadoop.graphReader=org.apache.tinkerpop.gremlin.hadoop.structure.io.script.ScriptInputFormat
gremlin.hadoop.scriptInputFormat.script=./data/script-input-grateful-dead.groovy
gremlin.hadoop.inputLocation=./data/grateful-dead.txt
gremlin.hadoop.graphWriter=org.apache.hadoop.mapreduce.lib.output.NullOutputFormat
gremlin.hadoop.graphOutputFormat=org.apache.hadoop.mapreduce.lib.output.NullOutputFormat
gremlin.hadoop.outputLocation=output
gremlin.hadoop.jarsInDistributedCache=true
janusgraph-grateful.properties
gremlin.graph=org.janusgraph.core.JanusGraphFactory
storage.hbase.table=grateful
storage.hostname=
run.groovy
outputGraphConfig = [path to janusgraph-grateful.properties]
:load ./data/grateful-dead-jansugraph-schema.groovy
graph = JanusGraphFactory.open(outputGraphConfig)
defineGratefulDeadSchema(graph)
graph.close()
readGraph = GraphFactory.open([path to hadoop-load-csv.properties])
blvp = BulkLoaderVertexProgram.build().writeGraph(outputGraphConfig).create(readGraph)
readGraph.compute(SparkGraphComputer).program(blvp).submit().get()
g = GraphFactory.open(outputGraphConfig).traversal()
g.V().count()
g.E().count()
After that I dropped the whole graph, subsampled the data and loaded it again, and it failed.
1,song,HEY BO DIDDLEY,cover,5 followedBy,2,1|followedBy,3,2|followedBy,4,1|followedBy,5,1|followedBy,6,1
2,song,IM A MAN,cover,1 followedBy,1,1
3,song,NOT FADE AWAY,cover,531 followedBy,5,572 followedBy,5,40|followedBy,1,2
4,song,BERTHA,original,394 followedBy,10,4 followedBy,1,1
5,song,GOING DOWN THE ROAD FEELING BAD,cover,293
6,song,MONA,cover,1 sungBy,3|writtenBy,5 followedBy,1,1|followedBy,2,1
7,song,WHERE HAVE THE HEROES GONE,,0 followedBy,8,1 followedBy,9,1
8,song,OH BOY,cover,2 followedBy,9,1|followedBy,3,1|followedBy,7,1|sungBy,5|writtenBy,4 followedBy,1,1|followedBy,7,1|followedBy,6,1
800,song,WINING BOY BLUES,cover,1 sungBy,5|writtenBy,4
9,song,HERE COMES SUNSHINE,original,65 followedBy,10,1 followedBy,6,2
10,song,HERE COMES SUNSHINE,original,65
I got a NoSuchElement Error and when I looked into the graph, g.V().count() returns 10 while g.E().count() returns 0.
Does anyone know what is happening? It would be very kind of you to give me some advice.