Exception in thread "Thread-2" java.lang.NullPointerException ObjectInputStream

Question

I am a beginner in java I am trying to make a communication with serialPort, however at the time of executing the method that receives data it throws me the error.

Exception in thread "Thread-2" java.lang.NullPointerException at Controlador.ControladorMain$4.run(ControladorMain.java:354) at java.lang.Thread.run(Thread.java:748)

I do not understand that it is failing, I have tried the code on another computer and there it does not throw the error I am confused, someone can help me.

public void receiveFile() {
    final InputStream in=serialPort.getInputStream();
    Thread t;
    t = new Thread(new Runnable() {
        @Override
        public void run() {
            System.out.println("listening...: ");

            while (true) {
                FileOutputStream file = null;
                ObjectInputStream out = null;

                try {                        
                    out = new ObjectInputStream(in);

                    if (view.jCheckBoxArchiboR.isSelected()) 
                        file = new FileOutputStream("File.txt");
                    else 
                        file = new FileOutputStream("content.txt");


                    byte[] buf = new byte[1024];

                    while (true) {
                        if (!view.jCheckBoxArchiboR.isSelected())
                           view.jTextAreaBinRecibido.setText(textoABinario(fileRead("content.txt")));

                        int len = out.read(buf);

                        if (len == -1) 
                            break;

                        file.write(buf, 0, len);
                    }
                    if(out.available()<1)
                        sendFile("ack.txt"); 

                } catch (IOException ex) {
                    ex.printStackTrace();
                    System.out.println("An error occurred while receiving the file");

                } finally {
                    try {
                    out.close();
                    } catch (IOException ex) {
                        ex.printStackTrace();
                    }
                }
            }
        }
    }
    );
    t.start();
}

line 354 where the error appears is this.

out.close();