output: #fixed code
                                @Test
    public void canAcceptAndReadData() throws IOException, InterruptedException {
      final AtomicInteger acceptCount = new AtomicInteger();
      final AtomicInteger readCount = new AtomicInteger();
      final AtomicInteger connectCount = new AtomicInteger();
      final AtomicInteger lastReadBytesCount = new AtomicInteger();
      final ByteBuffer byteBuffer = ByteBuffer.allocate(10);
  
      final Semaphore semaphore = new Semaphore(0);
  
      this.channelListener = new ChannelListener() {
        @Override
        public void onNewDataAvailable(SocketChannel socketChannel) throws IOException {
          readCount.incrementAndGet();
          lastReadBytesCount.set(socketChannel.read(byteBuffer));
          if (lastReadBytesCount.get() == -1) {
            socketChannel.close();
          }
          semaphore.release();
        }
  
        @Override
        public void onConnectionAccept(SocketChannel socketChannel) throws IOException {
          acceptCount.incrementAndGet();
          semaphore.release();
        }
  
        @Override
        public void onConnected(SocketChannel socketChannel, ConnectTask connectTask) {
          connectCount.incrementAndGet();
          semaphore.release();
        }
      };
  
      ExecutorService executorService = Executors.newSingleThreadExecutor();
      Future<?> future = executorService.submit(myConnectionManager);
  
      assertEquals(acceptCount.get(), 0);
      assertEquals(readCount.get(), 0);
      int serverPort = ConnectionManager.PORT_RANGE_START;
      Socket socket = new Socket();
      while (serverPort < ConnectionManager.PORT_RANGE_END) {
        try {
          socket.connect(new InetSocketAddress("127.0.0.1", serverPort));
        } catch (ConnectException ignored) {}
        serverPort++;
      }
  
      if (!socket.isConnected()) {
        fail("can not connect to server channel of connection manager");
      }
  
      tryAcquireOrFail(semaphore);//wait until connection is accepted
  
      assertTrue(socket.isConnected());
      assertEquals(acceptCount.get(), 1);
      assertEquals(readCount.get(), 0);
  
      Socket socketSecond = new Socket("127.0.0.1", serverPort);
  
      tryAcquireOrFail(semaphore);//wait until connection is accepted
  
      assertTrue(socketSecond.isConnected());
      assertEquals(acceptCount.get(), 2);
      assertEquals(readCount.get(), 0);
      socketSecond.close();
      tryAcquireOrFail(semaphore);//wait read that connection is closed
      assertEquals(readCount.get(), 1);
      assertEquals(acceptCount.get(), 2);
      assertEquals(lastReadBytesCount.get(), -1);
      byteBuffer.rewind();
      assertEquals(byteBuffer.get(), 0);
      byteBuffer.rewind();
      String writeStr = "abc";
      OutputStream outputStream = socket.getOutputStream();
      outputStream.write(writeStr.getBytes());
      tryAcquireOrFail(semaphore);//wait until read bytes
      assertEquals(readCount.get(), 2);
      assertEquals(lastReadBytesCount.get(), 3);
      byte[] expected = new byte[byteBuffer.capacity()];
      System.arraycopy(writeStr.getBytes(), 0, expected, 0, writeStr.length());
      assertEquals(byteBuffer.array(), expected);
      outputStream.close();
      socket.close();
      tryAcquireOrFail(semaphore);//wait read that connection is closed
      assertEquals(readCount.get(), 3);
  
      int otherPeerPort = 7575;
      ServerSocket ss = new ServerSocket(otherPeerPort);
      assertEquals(connectCount.get(), 0);
      myConnectionManager.connect(new ConnectTask("127.0.0.1", otherPeerPort, new TorrentHash() {
        @Override
        public byte[] getInfoHash() {
          return new byte[0];
        }
  
        @Override
        public String getHexInfoHash() {
          return null;
        }
      }), 1, TimeUnit.SECONDS);
      ss.accept();
      tryAcquireOrFail(semaphore);
      assertEquals(connectCount.get(), 1);
  
      executorService.shutdownNow();
      boolean executorShutdownCorrectly = executorService.awaitTermination(10, TimeUnit.SECONDS);
      assertTrue(executorShutdownCorrectly);
      executorService.shutdown();
      executorService.awaitTermination(1, TimeUnit.MINUTES);
    }
input: #vulnerable code 
                                @Test
    public void canAcceptAndReadData() throws IOException, InterruptedException {
      final AtomicInteger acceptCount = new AtomicInteger();
      final AtomicInteger readCount = new AtomicInteger();
      final AtomicInteger connectCount = new AtomicInteger();
      final AtomicInteger lastReadBytesCount = new AtomicInteger();
      final ByteBuffer byteBuffer = ByteBuffer.allocate(10);
  
      final Semaphore semaphore = new Semaphore(0);
  
      this.channelListener = new ChannelListener() {
        @Override
        public void onNewDataAvailable(SocketChannel socketChannel) throws IOException {
          readCount.incrementAndGet();
          lastReadBytesCount.set(socketChannel.read(byteBuffer));
          if (lastReadBytesCount.get() == -1) {
            socketChannel.close();
          }
          semaphore.release();
        }
  
        @Override
        public void onConnectionAccept(SocketChannel socketChannel) throws IOException {
          acceptCount.incrementAndGet();
          semaphore.release();
        }
  
        @Override
        public void onConnected(SocketChannel socketChannel, ConnectTask connectTask) {
          connectCount.incrementAndGet();
          semaphore.release();
        }
      };
  
      ExecutorService executorService = Executors.newSingleThreadExecutor();
      Future<?> future = executorService.submit(myConnectionManager);
  
      assertEquals(acceptCount.get(), 0);
      assertEquals(readCount.get(), 0);
  
      Socket socket = new Socket("127.0.0.1", ConnectionManager.PORT_RANGE_START);
  
      tryAcquireOrFail(semaphore);//wait until connection is accepted
  
      assertTrue(socket.isConnected());
      assertEquals(acceptCount.get(), 1);
      assertEquals(readCount.get(), 0);
  
      Socket socketSecond = new Socket("127.0.0.1", ConnectionManager.PORT_RANGE_START);
  
      tryAcquireOrFail(semaphore);//wait until connection is accepted
  
      assertTrue(socketSecond.isConnected());
      assertEquals(acceptCount.get(), 2);
      assertEquals(readCount.get(), 0);
      socketSecond.close();
      tryAcquireOrFail(semaphore);//wait read that connection is closed
      assertEquals(readCount.get(), 1);
      assertEquals(acceptCount.get(), 2);
      assertEquals(lastReadBytesCount.get(), -1);
      byteBuffer.rewind();
      assertEquals(byteBuffer.get(), 0);
      byteBuffer.rewind();
      String writeStr = "abc";
      OutputStream outputStream = socket.getOutputStream();
      outputStream.write(writeStr.getBytes());
      tryAcquireOrFail(semaphore);//wait until read bytes
      assertEquals(readCount.get(), 2);
      assertEquals(lastReadBytesCount.get(), 3);
      byte[] expected = new byte[byteBuffer.capacity()];
      System.arraycopy(writeStr.getBytes(), 0, expected, 0, writeStr.length());
      assertEquals(byteBuffer.array(), expected);
      outputStream.close();
      socket.close();
      tryAcquireOrFail(semaphore);//wait read that connection is closed
      assertEquals(readCount.get(), 3);
  
      int otherPeerPort = 7575;
      ServerSocket ss = new ServerSocket(otherPeerPort);
      assertEquals(connectCount.get(), 0);
      myConnectionManager.connect(new ConnectTask("127.0.0.1", otherPeerPort, new TorrentHash() {
        @Override
        public byte[] getInfoHash() {
          return new byte[0];
        }
  
        @Override
        public String getHexInfoHash() {
          return null;
        }
      }), 1, TimeUnit.SECONDS);
      ss.accept();
      tryAcquireOrFail(semaphore);
      assertEquals(connectCount.get(), 1);
  
      executorService.shutdownNow();
      boolean executorShutdownCorrectly = executorService.awaitTermination(10, TimeUnit.SECONDS);
      assertTrue(executorShutdownCorrectly);
    } 
                              #location 66 
                              #vulnerability type NULL_DEREFERENCE