private boolean hasKeyNotKnownAsProductive(final ValueTraversal child) {
        return productiveKeys.isEmpty() ||
                child.getBypassTraversal() == null && !productiveKeys.contains(child.getPropertyKey());
    }
Determines if the {@link ValueTraversal} references a productive key.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/strategy/optimization/ProductiveByStrategy.java