private String canonic(String attributeName, IndexFacts.Session indexFacts) {
        if (indexFacts == null) return attributeName;
        return indexFacts.getCanonicName(attributeName);
    }
Creates a new sorting from the given string and returns it, or returns null if the argument does not contain
any sorting criteria (e.g it is null or the empty string)
container-search/src/main/java/com/yahoo/search/query/Sorting.java