public void initAttributeNames(AttributesConfig config) {
        HashMap<String, AttributesConfig.Attribute> attributes = new HashMap<>(config.attribute().size());

        for (AttributesConfig.Attribute attr : config.attribute()) {
            attributes.put(attr.name(), attr);
        }
        setAttributeNames(attributes);
    }
Check sorting specification makes sense to the search cluster before
passing it on to the backend.

@author Steinar Knutsen
container-search/src/main/java/com/yahoo/prelude/searcher/ValidateSortingSearcher.java