return map.containsKey(o);
    }

    /**
     * Adds the specified element to this set if it is not already present.
     *
     * @param o
     *            element to be added to this set.
     * @return true if the set did not already contain the specified
     *         element.
     */
    @Override
    public boolean add(final E o) {
        return map.put(o, PRESENT) == null;
    }

            final long processingTime = systemHelper.getCurrentTimeAsLong() - startTime;
            docList.addProcessingTime(processingTime);
            if (logger.isDebugEnabled()) {
                logger.debug("Added the document({}, {}ms). The number of a document cache is {}.",
                        MemoryUtil.byteCountToDisplaySize(contentSize), processingTime, docList.size());
            }

                    docList.addProcessingTime(processingTime);
                    if (logger.isDebugEnabled()) {
                        logger.debug("Added the document({}, {}ms). The number of a document cache is {} (size: {}).",
                                MemoryUtil.byteCountToDisplaySize(contentSize), processingTime, docList.size(), docList.getContentSize());
                    }