// Take newer values from item2
        mergedItem.setTimestamp(item2.getTimestamp());
        mergedItem.setUserBoost(item2.getUserBoost());
        mergedItem.setEmptySource(item2.toEmptyMap());

        // Sum frequencies
        mergedItem.setQueryFreq(item1.getQueryFreq() + item2.getQueryFreq());
        mergedItem.setDocFreq(item1.getDocFreq() + item2.getDocFreq());

        return mergedItem;
    }