public static boolean isStartStep(final Step<?, ?> step) {
        return step instanceof GraphStep && ((GraphStep) step).isStart;
    }
Unrolls a single collection argument into an array of ids. This is useful for steps like
{@code g.V(['a','b','c'])}.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/GraphStep.java