Print Android, Bluetooh

The outPutStream object gives me error,

  

W / System.err: java.lang.NullPointerException: Attempt to invoke   virtual method 'void java.io.OutputStream.close ()' on a null object   reference.

is when I try to send the data

try {
            mmOutputStream.write(msg.getBytes());
            bluetooth.setText("Data Sent");
        } catch (NullPointerException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }