@Override
    public int compare(Hit first, Hit second) {
        if (secondaryComparator == null) return 0;
        return secondaryComparator.compare(first, second);
    }
Returns the comparison form the secondary comparison, or 0 if the secondary is null.
When overriding this in the subclass, always <code>return super.compare(first,second)</code>
at the end of the subclass' implementation.
container-search/src/main/java/com/yahoo/search/result/ChainableComparator.java