@Override
    public String toString() {
        return "FieldComparator:" + (sorting == null ? " null" : sorting.toString());
    }
Compares hits based on a sorting specification and values
stored in hit fields.0
<p>
When one of the hits has the requested property and the other
has not, the hit containing the property precedes the one
that does not.
<p>
There is no locale based sorting here, as the backend does
not do that either.

@return -1, 0, 1 if first should be sorted before, equal to or after second
container-search/src/main/java/com/yahoo/search/result/FieldComparator.java