@Override
    public int hashCode() {
        int result = super.hashCode();
        result = 31 * result + (value != null ? value.hashCode() : dateTraversal.hashCode());
        return result;
    }
Reference implementation for date difference step.

@author Valentyn Kahamlyk
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/DateDiffStep.java