private IndexNameExpander swapIndexCreator(IndexNameExpander newExpander) {
        IndexNameExpander old = indexNameExpander;
        indexNameExpander = newExpander;
        return old;
    }
The sorting specified in the YQL+ query last parsed.

@return a Sorting instance or null
container-search/src/main/java/com/yahoo/search/yql/YqlParser.java