#vulnerable code 
                                private void handleRestore(Operation op, RestoreRequest req) {
        IndexWriter w = this.writer;
        if (w == null) {
            op.fail(new CancellationException());
            return;
        }

        // We already have a slot in the semaphore.  Acquire the rest.
        final int semaphoreCount = QUERY_THREAD_COUNT + UPDATE_THREAD_COUNT - 1;
        try {

            this.writerAvailable.acquire(semaphoreCount);
            close(w);

            File directory = new File(new File(getHost().getStorageSandbox()), this.indexDirectory);
            // Copy whatever was there out just in case.
            if (directory.exists() && directory.listFiles().length > 0) {
                this.logInfo("archiving existing index %s", directory);
                archiveCorruptIndexFiles(directory);
            }

            this.logInfo("restoring index %s from %s md5sum(%s)", directory, req.backupFile,
                    FileUtils.md5sum(new File(req.backupFile)));
            FileUtils.extractZipArchive(new File(req.backupFile), directory.toPath());
            this.indexUpdateTimeMicros = Utils.getNowMicrosUtc();
            createWriter(directory, true);
            op.complete();
            this.logInfo("restore complete");
        } catch (Throwable e) {
            logSevere(e);
            op.fail(e);
        } finally {
            this.writerAvailable.release(semaphoreCount);
        }
    } 
                            #location 17 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                private void handleRestore(Operation op, RestoreRequest req) {
        IndexWriter w = this.writer;
        if (w == null) {
            op.fail(new CancellationException());
            return;
        }

        // We already have a slot in the semaphore.  Acquire the rest.
        final int semaphoreCount = QUERY_THREAD_COUNT + UPDATE_THREAD_COUNT - 1;
        try {

            this.writerAvailable.acquire(semaphoreCount);
            close(w);

            File directory = new File(new File(getHost().getStorageSandbox()), this.indexDirectory);
            // Copy whatever was there out just in case.
            if (directory.exists()) {
                // We know the file list won't be null because directory.exists() returned true,
                // but Findbugs doesn't know that, so we make it happy.
                File[] files = directory.listFiles();
                if (files != null && files.length > 0) {
                    this.logInfo("archiving existing index %s", directory);
                    archiveCorruptIndexFiles(directory);
                }
            }

            this.logInfo("restoring index %s from %s md5sum(%s)", directory, req.backupFile,
                    FileUtils.md5sum(new File(req.backupFile)));
            FileUtils.extractZipArchive(new File(req.backupFile), directory.toPath());
            this.indexUpdateTimeMicros = Utils.getNowMicrosUtc();
            createWriter(directory, true);
            op.complete();
            this.logInfo("restore complete");
        } catch (Throwable e) {
            logSevere(e);
            op.fail(e);
        } finally {
            this.writerAvailable.release(semaphoreCount);
        }
    }