private void wrapValueTraversalInCoalesce(final TraversalParent parentStep, final Traversal.Admin<Object, Object> child) {
        final Traversal.Admin temp = new DefaultGraphTraversal<>();
        temp.addStep(new CoalesceStep(temp, child.clone(), nullTraversal));
        temp.setParent(parentStep);
        ((ValueTraversal<Object, Object>) child).setBypassTraversal(temp);
    }
Validate that the {@link ValueTraversal} needs to be wrapped. It can be skipped if a bypass is already in place
or if there isn't a {@link CoalesceStep} at the start or if there isn't a {@code null} in the
{@link CoalesceStep}.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/strategy/optimization/ProductiveByStrategy.java