@Override
    public Configuration getConfiguration() {
        final Configuration conf = super.getConfiguration();
        conf.setProperty(PRODUCTIVE_KEYS, this.productiveKeys);
        return conf;
    }
Determines if the {@link ValueTraversal} references a productive key.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/strategy/optimization/ProductiveByStrategy.java