@Override
            public void onFailure(final Exception e) {
                deferred.reject(e);
            }
        });
    }

    @Override
    protected String getValidationError() {
        return null;
    }

    /**
     * Builds the OpenSearch query for popular words.
     * @return The QueryBuilder instance.
     */
    protected QueryBuilder buildQuery() {

     * Adds a language to filter by.
     * @param lang The language.
     */
    public void addLang(final String lang) {
        languages.add(lang);
    }

    @Override
    protected String getValidationError() {
        return null;
    }

    @Override
    protected void processRequest(final Client client, final Deferred<SuggestResponse> deferred) {