final OptionalThing<HttpServletResponse> responseOpt = LaResponseUtil.getOptionalResponse();
        final FessConfig fessConfig = ComponentUtil.getFessConfig();
        final int rankConstant = fessConfig.getRankFusionRankConstantAsInteger();
        final int size = windowSize / searchers.length;
        if (logger.isDebugEnabled()) {
            logger.debug("The searcher window size is {} and a rank constant is {}.", size, rankConstant);

     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     * @throws NumberFormatException When the property is not integer.
     */
    Integer getRankFusionRankConstantAsInteger();

    /**
     * Get the value for the key 'rank.fusion.threads'. <br>
     * The value is, e.g. -1 <br>
     * comment: Number of threads for rank fusion.