java.util.ConcurrentModificationException: null
at java.util.HashMap$HashIterator.nextNode(HashMap.java:1429)
at java.util.HashMap$ValueIterator.next(HashMap.java:1458)
at com.tinkerpop.gremlin.tinkergraph.process.graph.step.sideEffect.TinkerGraphStep.iteratorList(TinkerGraphStep.java:80)
at com.tinkerpop.gremlin.tinkergraph.process.graph.step.sideEffect.TinkerGraphStep.vertices(TinkerGraphStep.java:54)
at com.tinkerpop.gremlin.tinkergraph.process.graph.step.sideEffect.TinkerGraphStep.lambda$new$23(TinkerGraphStep.java:31)
at com.tinkerpop.gremlin.tinkergraph.process.graph.step.sideEffect.TinkerGraphStep$$Lambda$20/2139741886.get(Unknown Source)
at com.tinkerpop.gremlin.process.graph.step.sideEffect.GraphStep.generateTraversers(GraphStep.java:71)
at com.tinkerpop.gremlin.process.graph.step.sideEffect.StartStep.processNextStart(StartStep.java:58)
at com.tinkerpop.gremlin.process.util.AbstractStep.hasNext(AbstractStep.java:117)
at com.tinkerpop.gremlin.process.util.ExpandableStepIterator.next(ExpandableStepIterator.java:33)
at com.tinkerpop.gremlin.process.graph.step.branch.RepeatStep.standardAlgorithm(RepeatStep.java:160)
at com.tinkerpop.gremlin.process.graph.step.util.ComputerAwareStep.processNextStart(ComputerAwareStep.java:30)
at com.tinkerpop.gremlin.process.util.AbstractStep.hasNext(AbstractStep.java:117)
at com.tinkerpop.gremlin.process.util.ExpandableStepIterator.next(ExpandableStepIterator.java:33)
at com.tinkerpop.gremlin.process.graph.step.sideEffect.SideEffectStep.processNextStart(SideEffectStep.java:28)
at com.tinkerpop.gremlin.process.util.AbstractStep.hasNext(AbstractStep.java:117)
at com.tinkerpop.gremlin.process.util.ExpandableStepIterator.next(ExpandableStepIterator.java:33)
at com.tinkerpop.gremlin.process.graph.step.sideEffect.SideEffectCapStep.standardAlgorithm(SideEffectCapStep.java:56)
at com.tinkerpop.gremlin.process.graph.step.sideEffect.SideEffectCapStep.processNextStart(SideEffectCapStep.java:48)
at com.tinkerpop.gremlin.process.util.AbstractStep.next(AbstractStep.java:102)
at com.tinkerpop.gremlin.process.util.AbstractStep.next(AbstractStep.java:15)