private Item checkBlock(BlockItem b, StemContext context) {
        if (b instanceof PrefixItem || !b.isWords()) return (Item) b;

        if (b.isFromQuery() && !b.isStemmed()) {
            Index index = context.indexFacts.getIndex(b.getIndexName());
            StemMode stemMode = index.getStemMode();
            if (stemMode != StemMode.NONE) return stem(b, context, index);
        }
        return (Item) b;
    }
Replaces query terms with their stems

@author Mathias Lidal
@author bratseth
@author Steinar Knutsen
container-search/src/main/java/com/yahoo/prelude/querytransform/StemmingSearcher.java