code: public Object putIfAbsent(CacheKey key, Object value)
     {
        CompressedISPNChangesBuffer changesContainer = getChangesBufferSafe();
        changesContainer.add(new PutObjectIfAbsentContainer(key, value, parentCache, changesContainer.getHistoryIndex(),
           local.get(), allowLocalChanges));
        return null;
     }
docs: {@inheritDoc}