#fixed code
                                void close() throws IOException {
        writeLock.lock();
        try {
            if (isClosing) {
                // instance already closed.
                return;
            }
            isClosing = true;

            try {
                if(!compactionManager.stopCompactionThread(true))
                    setIOErrorFlag();
            } catch (IOException e) {
                logger.error("Error while stopping compaction thread. Setting IOError flag", e);
                setIOErrorFlag();
            }

            if (options.isCleanUpInMemoryIndexOnClose())
                inMemoryIndex.close();

            if (currentWriteFile != null) {
                currentWriteFile.flushToDisk();
                currentWriteFile.getIndexFile().flushToDisk();
                currentWriteFile.close();
            }
            if (currentTombstoneFile != null) {
                currentTombstoneFile.flushToDisk();
                currentTombstoneFile.close();
            }

            for (HaloDBFile file : readFileMap.values()) {
                file.close();
            }

            DBMetaData metaData = new DBMetaData(dbDirectory);
            metaData.loadFromFileIfExists();
            metaData.setOpen(false);
            metaData.storeToFile();

            dbDirectory.close();

            if (dbLock != null) {
                dbLock.close();
            }
        } finally {
            writeLock.unlock();
        }
    }
#vulnerable code 
                                void delete(byte[] key) throws IOException {
        writeLock.lock();
        try {
            InMemoryIndexMetaData metaData = inMemoryIndex.get(key);
            if (metaData != null) {
                //TODO: implement a getAndRemove method in InMemoryIndex.
                inMemoryIndex.remove(key);
                TombstoneEntry entry =
                    new TombstoneEntry(key, getNextSequenceNumber(), -1, Versions.CURRENT_TOMBSTONE_FILE_VERSION);
                currentTombstoneFile = rollOverTombstoneFile(entry, currentTombstoneFile);
                currentTombstoneFile.write(entry);
                markPreviousVersionAsStale(key, metaData);
            }
        } finally {
            writeLock.unlock();
        }
    } 
                            #location 11 
                            #vulnerability type NULL_DEREFERENCE