public static boolean isVariableStartStep(final Step<?, ?> step) {
        return step.getClass().equals(StartStep.class) && null == ((StartStep) step).start && ((StartStep) step).labels.size() == 1;
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/sideEffect/StartStep.java