protected CompositeItem createGramRoot(HasIndexItem term, Query query) {
        return createGramRoot(query);
    }
Creates the root of the query subtree which will contain the grams to match,
called by {@link #splitToGrams}. This hook is provided to make it easy to create a subclass which
matches grams using a different composite item, e.g an OrItem.

This default implementation returns createGramRoot(query).

@param term the term item this gram root is replacing in the query tree,
            typically used to access the index name of the term when that is required by the new gram root
            (such as in PhraseItem)
@param query the input query, to make it possible to return a different composite item type
             depending on the query content
@return the composite item to add the gram items to in {@link #splitToGrams}
container-search/src/main/java/com/yahoo/search/querytransform/NGramSearcher.java